[Preso]

How many words have been written on how many forums about the lack of rigidity in the Seig X3 vertical column? I have a Seig which was converted to CNC using a Promica kit back in 2011. Like everyone else, I was appalled at its inability to machine steel and although I have done some reasonable work in aluminium I thought it was about time I tackled the problem in a serious way.
I have read all the posts I can find on ways to combat the problem and I have considered lapping the column, scraping the gib, fitting a rigid frame around the machine and I have fitted a counterbalance. However, the real issue is the fact that the column must be open at the back so the motion of the ball nut can be transferred to the head via the side plates. Given the three sided nature of the column and the fact that there is not a lot of thickness in the casting, it is almost inevitable that there is going to be some bending and torsion as the cutter does its thing. In my view, the obvious solution is to completely fill the column and the base with epoxy granite. So what to do with the Z drive mechanism?
Before the Promica website and forum was taken down (damn! I had a really good post on there about the motor upgrade I did on my machine), there was a post by another user about how he had fitted the stepper motor and Z screw on the outside of the column. The poster claimed it worked just fine and unfortunately the information is now gone. So, I had to reinvent the wheel somewhat and this is the solution I have come up with.
The stepper motor (a 270oz Nema 23) is now moved to the top of the column complete with its 2:1 reduction belt drive.
Attachment 249722
The Z ball screw is inverted and the ball nut is fitted to the left hand side of the head using the original side plate as a mounting point. A new lower bearing mount is fitted to the bottom left hand side of the column and a 200n gas strut is fitted on the right hand side of the column. The limit switch is now fitted at the top right hand side of the column. While I am doing the upgrade I am also fitting double ball nuts to all the axes to try to eliminate as much of the backlash as possible.
Of course, this upgrade is a bit of a one way street. There is no going back once the column and base are full of epoxy and rock! To hedge my bets a bit I did a very crude lash up with some G clamps and some fabricated brackets as a sort of proof of concept. The photo here shows the first trial.
Attachment 249724
To my surprise the system worked as well as it did before (in the original Promica setup). At this point I did not have the spindle motor fitted so I reassembled the .75kw 3 phase induction motor and its bracket back on to the head which now had a mass of 35kg and made some slight improvements on the ball nut mount and the top motor bracket. Once again everything worked as it should and there was no sign of the Z motor losing steps or stalling. Both these trials were done with the counterweight removed.
Somewhat heartened by the trial I set about modelling the new hardware I would need on my CAD programme. The old Promica bearing mounts would be scrapped and new aluminium alloy castings would be used to replace them. The ball nut mount would be machined from stock alloy and a new channel would be machined to align the double ball nuts which are preloaded by fitting two wave washers in between them and then locking their location with M6 grub screws.
When I was fairly sure I had the design right I printed ABS prototypes of the new fittings and mocked up the drive in its correct location to check for alignment and interference.
Attachment 249726
It all looked good so I am now in the process of printing patterns for the upper and lower bearing mounts.
Of course, lifting the head from a point that is not symmetrical with the centre of the ways will be criticised but if you consider how just about every lathe carriage is driven along the bed using a lead screw and half nuts below and on the front of the bed it is pretty much the same scenario. Provided the gib strip is properly adjusted I cannot foresee any issues and in any case, it can't be much worse than the situation at present.
My machine was retrofitted with a large steel counterweight running via a cable because I was concerned about the added weight of the 3 phase motor I used to replace the original Seig motor. I intend to replace the counterweight system with a gas strut rated at around 20kg to provide some balancing force from the opposite side of the column. It is a fairly straightforward fit and I was always concerned about the counterweight fouling something on the rear of the machine.
The other concern that will be raised is the thought of the now exposed ball nut and screw picking up swarf, coolant and other contaminants. Not a good mix! I have purchased a bellows type leadscrew cover from a Chinese supplier on EBay which will need to be cut in half so that it can be fitted above and below the ball nut via some laser cut discs which can be clamped to both ends of the bellows.
Attachment 249716
For any Promica owners out there who purchased the single ball nut kit, retrofitting a second set of ball nuts is not as complex as I thought it was going to be. The biggest issue was sourcing the Thomson 7820827 ball nuts which are now listed as discontinued on the Thomson website. I managed to purchase three new ones from a seller on EBay and there may be an alternative from a different supplier that will do the job. I considered replacing all the screws and nuts but the cost was prohibitive. The original system used by Marc Huett to pre-load the double ball nuts seemed a bit complicated. My solution is based on some ideas I had seen on this forum which made use of a machined alloy channel which simply keeps the two ball nuts from rotating relative to each other. Since the Thomson nuts have a body 1" square it is a fairly simple solution, I will fit two wave washers in between the two ball nut bodies to establish the pre-load and then lock them in place with two grub screws. Here is the mock-up.
Attachment 249720

So, that is the plan. I will post some further updates and images as the build progresses.

[Fastest1]

I am watching. I would rather see a centered approach on the Z's screw but understand the difficulty with that.

[Preso]

Yep, like everything in engineering, there are always compromises. Here is a link to a Youtube video showing the second mock-up working with the spindle motor attached. https://www.youtube.com/watch?v=1htn...ature=youtu.be

[Preso]

Well, That didn't work!
My plan to fit two wave washers between the double ball nuts as a measure to introduce pre-load was a fail. As luck would have it, when I fitted the ball nuts to the screw, back to back, the space between the ball nuts was either less than nothing or around 5mm. Trying to fit multiple wave washers was an exercise in frustration since one or all would slip into the thread of the screw or they would all stack together which provided no pre-load at all. I will try to use a strongish spring instead. Or maybe a thick O ring?
Attachment 249986
Today I made some progress on the remaining parts, that is, the upper and lower bearing mounts. I have my own home foundry for casting aluminium alloy parts and given that my nice CNC mill is now in pieces it seemed logical to make these two parts as castings rather than trying to fabricate them. I modified the CAD models of the parts I had previously printed on my 3D printer to include the 2.5^o of draft and machining allowance and printed new parts to provide the patterns for the sand mould. The resulting castings were mostly sound. I did find some porosity on what was the top surface of the pattern but these surfaces are bolted against the column anyway. The photo below shows the original ABS prototype print on the left, the painted patterns and the unmachined castings on the right.
Attachment 249988. The next step was to machine the castings on my manual mill and lathe. The pockets have been machined for the angular contact bearing at the top mount and the plain ball bearing at the bottom.
This photo shows the finished top bracket and the old Promica one which will now be discarded.
Attachment 249990 I will be powder coating all the new parts in a wrinkle finish black. I have also modified the side plates which were originally for connecting the head to the nut inside the column. These turned out to be cast iron, not ground steel as I thought they would be. I cut off the "ears" with a hacksaw and milled the edges reducing the width of the plates to 70mm. The one on the right will have the ball nut holder attached with two M6 cap head screws and the one on the right will be used to attach the top of the gas strut and the interrupter "flag" for the opto limit switch. At this point I really am committed to the upgrade. Before I pulled out the hacksaw it would have been possible to reverse the build. If it all goes pear shaped now I guess I will be making new side plates
Attachment 249992
Tomorrow I hope to get the complete screw and motor system refitted to the column and if the test run is successful I will strip the machine and start the process of filling the base and column with epoxy granite. While I am at it I may lap the sliding surfaces and scrape the gibs if necessary

[Preso]

Success! Today I was able to finish the last of the machining on the castings for the upper and lower bearing mounts. The double ball nuts were fitted to the nut holder and the cap screw holes were transferred to the left hand side plate. Two M6 cap screws hold the nut holder to the side plate and the original M6 cap screws and dowel pins are used to fix the side plate to the head. Now it was necessary to align the ball screw with the vertical column so the upper and lower bearing mountings could be fixed in place, also with M6 screws. What followed was a lengthy period of measuring the offset of the screw from the front edge of the column. What I really needed was a depth micrometer but alas, I don't have one - yet! So with lots of bad words I used my digital caliper to measure between the front edge of the column and the face of a vee block that was pushed up against the screw. I already had the upper bearing mount lightly clamped to the top of the column and by measuring at the ball nut and at the top of the screw I managed to get the alignment to within .01mm. I was then able to transfer all the mounting holes and tap them. The pic below shows the finished assembly.
Attachment 250080 The lower bearing mount was fixed in place after the head, and the ball nuts were lowered all the way to the bottom of the screw. My thought was the the screw would automatically align the bottom bearing. It was clamped in place and the head run back to the top of the screw. All seemed well so the bottom bearing mount was fixed in place.
Attachment 250082
Now was the moment of truth. I reassembled the stepper motor and the 2:1 belt drive and used Mach3 to power the head up and down over it's full range. Once again there was no hesitation from the drive. The gib was already fairly tight and although the spindle motor was removed at this stage there was no counterweight either so essentially the screw was lifting the full 25kg of the head with no problems.
Next I fitted the gas strut with the top ball joint attached directly to the top of the right hand side plate via an M8 tapped hole. The lower ball joint needed a small spacer to correct the alignment of the strut. Another test run and on this one the stepper drive sounds a lot less "throaty" on the upward move. It was effectively only moving 5kg with the other 20kg being lifted by the strut.
Attachment 250084
Now I will remove the head and fill the base and column with epoxy granite. I will post some pics of this as soon as I can get some more epoxy.:cheers:

[Preso]

Now that I am committed to the idea of filling the column and base with epoxy granite I moved on with prepping these parts starting with the base. Before I could mix and pour the epoxy I had to consider how to manage the wiring for the motors and home switches. In the original Promica kit, the Y axis motor and home switch wires were routed through to the rear of the column via the hole where the Z screw handle and shaft emerged from the right hand side of the base. The Promica kit came with a machined aluminium disc with the correct size hole for the corrugated conduit to fit into. I had to provide a conduit all the way through to the rear of the base for these wires and luckily a piece of 1/2" copper water pipe was just the right size. I modified the original aluminium disc to include a press fitted socket for the split plastic corrugated conduit to attach to. This along with all the castings and new fittings were powder coated with a wrinkle finish black. This stuff is much more durable than paint. It is coolant proof and really easy and quick to apply. The best investment I ever made in workshop equipment! Better still I can now purchase the powder from a local supplier for a fraction of the cost I was purchasing it for from my previous supplier. Now I pay AU$15 per kilo.
Attachment 250442 This pic shows the entry point for the Y axis wiring with the powder coated finish.

The last job before filling the base was to make a timber mould to allow access to the socket head screws used to hold the Y axis nut down to the base. I used a technique on my drilling machine base where I made a tapered timber plug which was held in place by wood screws through the mounting holes you need to provide access to. A mould release of silicone grease allows the plug to be knocked out later. Finally I sealed up any remaining gaps with a water based sealer and allowed it to dry while I started on mixing the epoxy.
Attachment 250444 Here you can see the wooden plug before it is mounted via two wood screws. I ground the area where the plug fits to ensure a reasonably good seal.

I read lots of forums regarding the mixing ratios, ingredients and treatment of epoxy granite fills for machine builds. The conclusion I eventually came to was the there were lots of builders who were over-thinking the process. I my view all you need is some clean gravel and two grades of sand (fine and coarse) and a suitable epoxy. I used a simple spreadsheet to calculate the volumes by weight and I usually mix about 150 grams of resin at a time. It took about 8 mixes to completely fill the base. I know it doesn't look as pretty as some of the material that has been used to make a complete lathe bed or router table but given that it is completely hidden, who cares?
Attachment 250446 Here you can see the base half full.

Tomorrow I will fill the column and then I will have to struggle with getting the base and column back up on to the steel pedestal.

[H500]

Interesting. I can't wait to see it in action.

[Preso]

Progress!
Today I was able to prep the column for filling with epoxy resin. I plugged the holes that I had made to attach the top bearing bracket and levelled the column on a trestle in preparation for the final epoxy granite fill.
Attachment 250902All was running smoothly when a friend dropped by to say hello and check on the progress of the build. We chatted for a while and when he left about an hour later I went back to check if the epoxy had started to go off. Horror! There were two puddles of leaking resin on the floor. One was coming from a hole which had penetrated the top dovetail vee. It had been there from the start and I had not noticed it (since I didn't drill it.) The other more serious leak was coming from the bottom of the column where it is bolted to the base. Evidently there is a void in the bottom of the casting around 1.5mm thick and that too had escaped my attention. It was too late to do much apart from mopping up the leaking resin since I couldn't lift the machine off the trestle and getting access to both leaks was just about impossible. As it turned out I would have lost about two or three tablespoons of liquid resin so I am guessing there are a few voids in the epoxy granite fill around both the leaks.
Attachment 250904 In this pic you can see the resin dripping out of the lower column flange joint.
By mid afternoon the resin had solidified and I was able to lift the machine vertical again and give it a good clean and refitting the head back on to the vertical slide. I had previously lapped the gib and found that just over half of the gib had never been bearing on the inside of the dovetail. I was able to get about 90% contact without losing all of the adjustment in the gib. Most of the non contact area now hangs out the bottom of the dovetail in the head anyway. With that heavy unit back in place I placed a sling around the machine to hoist it back on to the machine cabinet.
Attachment 250908
My problem is that I have a one tonne chain hoist to lift the machine but once on the machine base I had to move it around four metres to where it lives in my workshop. The only option was to "waltz" it across the concrete floor, rocking it from one foot to the other whilst negotiating a path around some other closely spaced machines, and a car. Not good if you have a crook back.

I have covered what was the open back of the column with a 1.5mm thick aluminium sheet. It is a bit scratched but I will powder coat it later, if I can get access to a bigger oven. Come to think of it, that is probably the next project. The cover is purely cosmetic. I will also have to find a way of attaching the variable frequency drive to the column. It was previously fitted to the black steel cover that housed the original switch panel and power supply for the DC motor. I discarded all those items when I converted the motor to a 3 phase induction unit but I kept the original cover in place to keep dust and swarf out of the stepper motor drive an ball screw. With the drive now on the outside of the column I will ditch the black steel cover all together. The machine now looks a bit naked and flimsy with just the cast iron column holding up the head but it certainly feels solid, and heavy, now!
Attachment 250906 Here you can see the aluminium back which covers the rather untidy looking epoxy granite fill. Two sets of holes towards the top will be used for a bracket to support the VFD.

My next step is to refit all the vertical drive components and then add the extra set of ball nuts to the X and Y axes. I have a new idea for getting preload springs in between the double ball nuts. If I can work out how to model the springs in my CAD programme I will post details shortly.

[Preso]

Today I was able to reassemble most of the Z drive and the spindle motor assembly. Because I was retrofitting my system with double ball nuts I was looking for a way of providing preload between the opposing ball nuts. I tried and failed to fit wave washers and I toyed with the idea of using a single spring between the backs of the square ball nut bodies. The biggest issue was the limited space to fit even a few coils of a single spring. I recalled that I had used a series of small diameter springs to provide preload on the spindle of my Quorn tool and cutter grinder. With that in mind I laser cut a 3mm thick acrylic spacer with four holes at the corners to take some 5mm OD compression springs. The idea was that as the ball nuts were wound together on the screw, the springs would gradually compress to push the ball nuts against the opposite sides of the screw flanks where they could be locked in place with M6 grub screws. The acrylic spacer is there to stop the springs buckling and slipping out of alignment.
Attachment 250996 Here is a model of the idea.
In practice it is really hard to hold four springs in place as the ball nuts are wound together and in the end I used just two at diagonally opposite corners. When the ball nuts and spacer are placed inside the aluminium channel everything self aligns and the plastic spacer is positioned so that it cannot rub on the screw. I was able to reconnect the stepper motor to the controller and even with the full weight of the head, spindle drive, quill and covers in place the head drives up and down the column with no hesitation whatsoever. I even have the gib tightened on the very firm side. So, in respect of having some reservations about the offset screw binding the ways of the Z column, I am very happy.
With respect to having reduced backlash in the drive I am not so happy. I can move the Z pulley around 5 degrees either side of centre before the play is taken up in the drive. It is much better than before but definitely not zero. I was using backlash compensation on the X and Y axes and I was hoping to do away with the need for it in the new setup. I am hoping to get the rest of the ball nuts in place next week and start cutting material to see how rigid the new arrangement is. My gut feeling is that it will be a huge improvement. I gave the head a good whack with a soft faced mallet today and there is no sign of oscillation or deflection but this is hardly a definitive test!

[Preso]

So Close....
Today I was able to make some more progress on the build after something of a hiatus while I fixed the sagging roof insulation in my shed. I have fitted the VFD with some powder coated brackets but I am not happy with the positioning. I think the quill handle will foul the sheet metal enclosure of the VFD. The box was previously mounted on the side of the original Sieg motor power supply enclosure which was mounted on the back of the column. Now that I have scrapped this part the VFD was mounted further forwards with it's back flush with the rear of the column. I will probably need to rethink the positioning which probably means making new brackets!
Much more successful was the fitting of the double ball nuts to the X and Y axis screws. My plan to use the same method as I had used on the Z axis was a big fat fail. There simply wasn't enough clearance to use the machined channel to align the two ball nuts. I had to resort to a method similar to what Marc Huett had originally designed for the Promica kit. I machined up two alloy blocks with threaded holes to fit the Thomson ball nuts to. The Promica solution for providing the pre-load was to jack the two ball nuts apart using hex headed screws bearing on three M5 socket headed screws which protruded through one of the alloy ball nut mounts. Since I was too lousy to go and buy six M5 screws I machined up some stainless steel pillars from 10mm round rod. These were shouldered so that they would slide into the three holes in one of the blocks and were pushed away from the first ball nut with three co-linear M6 grub screws. It was a bit fiddly to fit but eventually I got everything aligned and locked down. It was a relief to have all the major components back in place however I initially thought I had wasted all the effort. I still had significant backlash in the Y axis despite all the effort. It just didn't make sense. The ball nuts were firmly pushed onto opposite flanks of the screw and everything was locked down as it should be. Finally the penny dropped. Marc Huett had originally allowed for three 10mm washers to be used to take up the slack between the face of the angular contact ball bearing and the 20T drive pulley. When I had a close look I realised that three washers were not thick enough to take up all the clearance. The 20T pulley was not pushing all the way against the inner race of the angular contact outer bearing. I slipped an extra washer onto the end of the ball screw and hey presto, almost no backlash! I will replace these four washers with a machined spacer as I figure that each interface between the washers is a source of movement in a system where you don't want to have any movement at all.
Attachment 251862 This image shows the original assembly diagram from the Promica Kit manual. I am guessing that most of my issues with backlash in the X and Y axes were due to not having sufficient spacing with just three washers as recommended in the manual. I had to resort to backlash compensation in Mach 3 which, frankly, is a pain in the butt. It slows down machining time and makes it almost impossible to machine accurate circular pockets.
Attachment 251864 Here is a pic of the newly fitted double ball nut assembly on the Y axis.
Attachment 251866 Here is the X axis assembly prior to the final fit up.
Tomorrow I hope to refit all the stepper motors and limit switches and get on with testing the system.

[Preso]

Hurrah!
Today was the big push to get the machine back together so that I could finally see if all the work was worth the effort. As luck would have it I screwed the final wire down at around 5 pm - on a Sunday afternoon and the Japanese Grand Prix was on so testing will have to wait until next week.
I fitted Z axis home switch to it's new location which is now on the outside of the column adjacent to the double ball nut cover. I machined slots in all the fittings so that it was possible to fine tune the alignment and position of the sensor and the "flag" that creates the home position. These parts were powder coated in wrinkle black like the castings for the Z drive.
Attachment 252044 New home switch position for the Z axis

Now imagine several hours of frustration tying to get the whole system to actually home. I checked and rechecked all the wiring, re-terminated all the plugs and went over the Mach3 settings at least five times. Finally I pulled the IC3A controller onto the workbench to look for a blown fuse when I noticed that the A axis home plug had been fitted incorrectly. I don't have a home switch on my fourth axis so I have a dummy plug fitted with a link wire but since it was fitted upside down the system was having a hissy fit. With all the motors and home switches functioning properly again I turned my attention to the positioning of the Variable Frequency Drive (VFD) housing.
Attachment 252040 This pic shows the mounts for the VFD enclosure and the new mounting point for the top of the gas strut.

I didn't like the way I had fitted the enclosure previously. The two straps across the back of the column looked a bit dodgy so I machined up two aluminium tubes with M6 studs running through them. A flat aluminium plate was drilled with the spacing I needed and this was used as a drilling template for the two mounting holes in the side of the column. It also served as a strengthening plate on the inside of the sheet metal enclosure. The box was now fitted a little further back on the column and a little further away from the quill handles. All the parts were powder coated in gloss black and the spindle wiring completed.
Attachment 252042 Here is the cheap and cheerful solution to the bare aluminium cover on the rear of the column.

I also wimped out on the idea of powder coating the aluminium cover on the back of the column. Adhering to the KISS principle (Keep It Simple Stupid) I covered the sheet aluminium with some self adhesive black vinyl. It cost $4 and looks just like satin black powder coat. Cool!
I found that the upper mounting position of the gas strut was not allowing the spindle to get close enough to the table. In it's lowest position there was still about 60mm gap between the face of the ER40 chuck and the surface of the table. With a short end mill in the chuck it was conceivable that I would not be able to machine a thin plate attached directly to the table. So I sacrificed a little upper height by mounting the top joint of the strut right at the top of the right hand side plate. This gives me enough downward travel and I figure I might never need the full height under the spindle anyway.
Attachment 252046 Here is the finished product less the Z axis ball screw cover which will require some extra fittings to couple it up to the exposed sections of the screw.

Sadly I did not get a chance to actually cut some metal after cleaning up and fitting all the loom tubes, sweeping the floor and putting all the tools away. I have some family duties to attend to over the next couple of days but I intend to give it a good work out and report the results.

[Preso]

The End is Nigh.
Today I made some progress with the swarf cover for the Z axis screw and ball nuts. I purchased a bellows type cover from a supplier on Ebay. It looked like it was made of rubber in the photo but it turned out to be made of a fabric reinforced vinyl with steel rings to create the concertina pattern in the tube. It was easy to cut into two lengths, one for above the nuts and one below. My idea for fitting it was to print some ABS collars which would allow the open ends of the bellows to be clamped either side of the ball nuts and at the underside of the top bearing mount and the top of the lower bearing mount. I did print three of these fittings but since there was an exposed thread on the lower ball nut I decided to turn an aluminium collar with a matching thread and screw this on to form one of the mounting collars.
Attachment 252334 Here you can see the aluminium threaded collar which will allow the bellows to be clamped below the ball nuts. I did away with the coil springs between the ball nuts to provide preload and used a thick O ring instead. It provided just enough pressure (along with the square acrylic washer) to eliminate the backlash.

I did have the brilliant idea to print a slip on fitting that would wrap around the ball nut mount that was screwed to the side plate of the head.
Attachment 252336 The top two parts are printed ABS fittings which slide on to the aluminium ball nut mounting. The reason for printing the two parts separately is to allow them to be printed without having to have any support material during the print. The collar is slipped into the hole from underneath and is held there by the chamfered flange.

This would mean that I didn't have to drill and tap any holes in this part and for a while, (a brief while), I thought I was pretty clever. It slipped on with a nice snug fit and the bellows slid on nicely but when I remounted the Z screw onto the column I realised that the home switch sensor body was going to foul the ABS mounting. Not by much but as you would expect it was just enough to make me scrap the part.
Attachment 252338Here is the fully assembled collar for the bellows. Looks neat but there is a problem!

Attachment 252340Here is the problem! The home switch sensor body will foul the 4mm thick ABS printed part around the outside of the ball nut mount. I have modified the part to allow clearance and it will still slide on the way I intended.

Such is the way of things when you work of partially completed CAD models. I have since modified the CAD part and will print a new one tomorrow. I was able to run the head up and down almost its full length of travel and although the bellows bunches up in a slightly erratic fashion it will serve the purpose of keeping chips and swarf out of the moving parts of the screw and nuts.
Attachment 252342Here is the finished bellows. I will print some clamps for holding the ends of the bellows to the collars. The zip ties don't really float my boat but they served the purpose of allowing me to test the range of movement I could get. I will also print a cover for the Z belt drive and fit that tomorrow.

This is a pic of the OrdBot Hadron 3D printer I use to rapid prototype all my ABS parts.
I fabbed all the metal parts myself and powder coated all the aluminium parts in translucent red sparkle. No-one was more amazed than me when it all worked as advertised!
Attachment 252344

[Preso]

Finished!
Yesterday I cut metal for the first time since completing the upgrade. The results were encouraging although there is still some vibration which gets transmitted through the whole machine and ends up rattling the door of the cabinet stand. However, while I was running a pocket process on a 40mm square block of aluminium fixed in a machine vice I held my hand on the side of the head and there was only a slightly perceptible movement. Certainly it was nothing like I had to put up with before. Today I ran another programme consisting of an outside profile roughing process, a finishing pass, a circular pocket roughing and a finish pass on the inside. The finish was as good as I would want on a machine of this type and I have been able to run depths of cut four times what I was using before.
The accuracy has improved as well. I have not bothered setting backlash compensation now that I have double ball nuts on all the axes. The error on the circular pocket was 0.02mm however the outside profile was 0.28. This seems a bit odd given that I did a 0.25 climb finishing pass on both the pocket and the outside profile. Clearly there is room for some diagnostic work ahead.
Attachment 252830Here is the finished part. I used a two flute 8mm end mill at 1500rpm, 400mm/min. and 2mm DOC.

Attachment 252832 This shows the inside diameter of the pocket which was 22mm in CamBam. Before the upgrade it was common to gradually increase the NC code diameter by up to 0.6mm to get it to machine at the correct size. With an error of 0.01 in one pass I am quite happy.

Attachment 252834 This result is not so good. The outside profile should have been 28mm. The funny thing is that the error is quite consistent at all points of the square profile. I will have to repeat the test to see if I got something wrong in the code.

So, was it worth it? I do believe that I will gradually dial in the machine to get better results and improved accuracy. I am only an amateur machinist at best. I generally break my fair share of tools and make plenty of scrap, but it's an enjoyable hobby just the same.

[HawkJET]

Preso, VERY NICE!

I have an X3 from Grizzly and plan to convert to CNC in much the same way you have. However my plan is to move the Z axis lead screw to the center of the column rather than the side as you have. I will be modifying the column extensively as well as the dovetail slide.

The thing I really like is that you filled the column and base of the machine with epoxy granite. I plan to do the same. The mechanical design of that part of the machine leaves much to be desired, so the epoxy granite should cover a multitude of those sins.

I agree with your comments about over-thinking the aggregate size ratios. Your approach probably achieves the desired outcome very well.

Thanks for posting this, it encourages me to get going on my own machine.

[Preso]

Now I Can Cut Steel!
Today I began a project I had been putting off for some time. I wanted a ball turning attachment for my Colchester lathe.
Attachment 254688 This is the model of the ball turning attachment. There are three fairly hefty steel profiles required.
I did the design and drawings last year but put off the construction because I would need to profile some 20mm thick hot rolled steel section. The shapes were not easily cut on a manual mill and I did not fancy flame cutting them and cleaning up with files etc. Machining on the X3 was a possibility but before I did the upgrade on the column and base of my machine I would not even consider it. The only time I tried to cut steel of any size it all ended in tears. As a bit of an experiment I saved the 2D drawings of the parts as DXF files and imported these into CAM BAM. I worked out a simple profile toolpath and ran it dry in Mach3. I had some 12mm roughing end mills and figured if it all went pear shaped I would not be smashing my one and only cutter of that size. I was running the cutter at 500 RPM with a .75mm DOC and a feed of 300mm per minute. Imagine my surprise when the job finished, albeit slowly, with a good surface finish and no broken teeth. During the cutting I even felt like overriding the feed as there was very little chatter. I have the feeling that the column and base are more rigid now than when I first reassembled the machine. Maybe the resin is still curing? I will post some photos tomorrow.

[Preso]

Success! (Slowly)
Today I was able to finish the most tedious parts of the machining required to make my ball turning attachment. I had three pieces of 75X20 hot rolled steel which had been set aside to make this attachment since last year but as I said in my previous post I did not fancy cutting them out manually nor did I hold out much hope that my Sieg X3 would ever be man enough to do the job. I decided to bite the bullet anyway. I wanted to mark out the parts just to make sure I had machining allowance on all the surfaces and also as a sort of sanity check when verifying the machining process. Because I design all my parts in a CAD programme (Autodesk Inventor) I export the drawings as DXF files. These can be opened in Corel Draw (or Inkscape) for editing and from there I can open them in CAM BAM. I also open them in LaserCad so I can mark out my steel blanks. I paint the surface of the steel with white acrylic paint and then vector engrave the paint in my 40W laser. I can then witness mark all the arc centres and edges.
I must stress that I was being deliberately conservative with the depths of cut that I used. As it was, the first cut that I did failed because I did not clamp the part down tightly enough. Each successive pass moved the stock sideways by about 0.5mm but I was able to stop the process on the 4th pass and reset the home point which cleaned up the fault.
Here is a clip of two of the machining processes and some stills of the finished cuts and parts>


I am pleased with the results. I didn't think I would ever be able to cut steel on this machine. Certainly not steel of this size anyway.

[blkexp98]

looking good. I have been wanting to convert to cnc for a while now and have been reading over all the info I can find on improvements before I take the plunge. Your idea is really interesting and your video shows it has merit. Have you seen any issues with the z axis screw being on the side? Are there any changes you would have made knowing what you know now? In some ways i can picture the offset ballscrew being an issue but at the same time don't think it will make any difference unless the z gib is too loose. If thats the case thats a problem in itself.

[Preso]

Since completing the upgrade I have started building a model Stirling engine and have so far completed around 70% of the machining. A lot of the parts were in either cast or billet aluminium alloy. Around half of those parts needed machining on the Sieg. So far the machine has performed flawlessly. (Oh, one tool crash - when a piece of waste fell into the back of the Y axis and jammed there. The tool plunged straight into one of the hardened steel clamps. To it's credit the 8mm HSS end mill chewed a sizeable chunk out of the clamp before it disintegrated!) I have not noticed any issues with the Z drive being off centre of the column. I can't think of anything I would have done differently in terms of the upgrade. I have since fitted a mist coolant system which does a great job of clearing the tool path. Perhaps if I had the space around the machine I would fit an enclosure. At present I get some serious mess which needs constant sweeping up. The wife approval factor is very low when she keeps finding aluminium chips in the house.