[dracozny]

I figure I should start trying to lump all my work into one thread at some point. Might help someone in some way even though there are plenty of spectacular builds here on the zone already.
progress so far:

• http://www.cnczone.com/forums/bencht...placement.html
• http://www.cnczone.com/forums/servo-...al-servos.html
• http://www.cnczone.com/forums/servo-...direction.html

I have actually had to use this mill as a lathe to work on those encoders, damn ugly. but just accurate enough to get the job done.

After mulling over pro's and con's I did order some ball screws from Chai, asked him to please make sure the wrapping was stiff and extra bubble-wrap and also found out DHL refuses to ship anything marked as fragile. nice to know. His English is pretty darn good compared to anyone else I have dealt with in China. Total cost for doublenuts with the lengths I requested was $226

I figure some people are having a hard time with their ball screw designs ( I know I did a lot of thinking about mine) so I will post up my crude drawing (really I just copied a picture and relabeled all the dimensions) *!note! - do not use these designs as is! You will still need to come up with your own measurements.

I basically measured the length of travel that I wanted to maintain or extend and used that to adjust the length needed. Then you have to add in your machined ends overall length so if you look at mine you can actually deduct the l1-5 measurements from L and you will see what my adjusted travel is. This isn't a true travel since Y and Z have physical limitations caused by the column, saddle, ways, and way covers.
I did use jid2's drawings for inspiration since he was kind enough to post them up for another user. So you can see that I stuck with the 1/2" ends for the pulley's I did not use the same lengths however.
My threads for the locknuts I chose based on the need for two lock nuts on each axis (after much reading I discovered that those locknuts Chai provides sometimes want to move, although I have not seen another user complain of this since 2010 so two is probably an overkill safety measure). The l3 length is based on the width of each bearing + the oil seals + 5mm space between each bearing. I kept the overall length of l3 short by 2mm in order to ensure I could preload the AC bearings by the locknuts. The length of l1 is to ensure I have enough distance from the bearing mounts to clear the Xaxis ways on the Y saddle. and for simplicity sakes I kept that length for all 3.
Z was a completely different beast I went with a heavier ballscrew so as a result I had to order larger bearings so combine that with my previous explanation and you will realize why the l3 lengths are different. Now the overall length I needed probably did not need the floating end to be mounted but I figured cheap insurance.

I ordered some timing pulleys this morning from https://sdp-si.com/ however I will need to either modify my servo shafts (they are 14mm) or modify the two pulleys. Since I do not have a lathe, I will probably just use the same method of modification I did on the rear shafts for the encoders and on the Spindle motor. The old 14mm shafts are not easy to find pulleys for at least not in a dimension I wanted.
I decided on a 2.63:1 ratio and sticking with what they had in stock made it challenging I wound up getting pulleys with a GT2 5mm pitch, these will take a 15mm wide belt. I will order the belts when I am sure of the lengths needed. The critical thing about pulleys is one getting them to match up to your desired speeds as well as still providing clearance from the table. I plan on making my belt covers and bearing mounts look like an integral part of the table much like what jid2 did although he had a few snags with the pulleys diameters being a tad too large to clear properly.

well that's all for now. I am just waiting for more parts to show up at my door.

[dracozny]

Well I got my Ball screws from Chai. I think I have to start with the bad side on this.

• Did not package it anywhere near expectations even after offering to pay for the extra packaging. the ball nuts had actually penetrated the cardboard.
• Z and Y screws seem to be lacking preload, the spacers just slop around and the ball nuts shift around from each other.
• I find it strange that the lock nuts are no longer the square nuts which throws me off when it comes to matching them up to my drawings. thankfully the Z threading is just long enough that only 1/8th inch or so hangs over.

On the plus side

• The machining looks good and appears to be within tolerance.
• There are no dents, dings or bends as a result of the pitiful packaging

so the immediate question is how to deal with fixing the Preload on the Y and Z screws.

[dracozny]

Slow work in progress. got my Z screw almost ready to go onto the mill. I wound up making a combination of spacers and bellville washers to fix the Z ball screw. I caked the lower half of the ball screw nut in grease and packed the balls into it and then screwed it back on. went pretty easy compared to some of the other methods I have seen.
here is a shot of some of the stuff I machined manually.

I wound up cutting that flange off on the Z motor mount, Apparently I did not realize I had it upside down. machined out a motor flange that bolts ontop and slides to adjust tension. probably the better way to do it anyways.



yup, that's duct tape, and yes it's very temporary.


I'm still waiting on the M6-4mm tube fittings for the ball screw before I can mount it up in the column. I'm also going to need to widen the channel for the ball screw nut mount. I thought about making the mount narrower but if you saw the hack job that makes that channel you would understand my decision to widen it and clean it up.

[dracozny]

On a negative note after wiring up the majority of the hardware I discovered that the Encoders I bought from US Digital back in September do not function. The encoder that came with the motor you see in the above picture however does work. So I know my wiring and 7i77 card work just fine. Fairly disappointing considering the cost. There is a 2 year warranty and I am waiting to hear back from US Digital on that issue.

on a plus side I have the Z motor and the Huanyang VFD working. was a bit of a challenge with Linuxcnc since the pncconfig did not generate the code correctly. things to point out for those who want to use linuxcnc with a Huanyang VFD (not using the serial interface) it's advisable to use a couple relays for the spindle on function and for the reverse function(assuming you need it).
some code to change in your hal file:
net spindle-vel-cmd-abs => hm2_5i25.0.7i77.0.1.analogout5
changed to
net spindle-vel-cmd-rpm-abs => hm2_5i25.0.7i77.0.1.analogout5

you will also want to add this to turn the spindle on and off. that pin is wired to the on/off relay. which connects the DCM to FOR or REV through the other relay. (you might have this part automatically generated by pncconf already if you specified this function)
net spindle-on => hm2_5i25.0.7i77.0.0.output-09

This other part you can do in the ini file or within Pncconf. The Max spindle speed and not the operating voltage is to be specified.

[SPINDLE_9]
OUTPUT_SCALE = 3600.0
OUTPUT_MIN_LIMIT = 0
OUTPUT_MAX_LIMIT = 3600.0

[dracozny]

Update: turns out those encoders were just fine. after contacting US Digital, I did a resistance test on a few pins that deal with 5v supply and it turns out I had a pin in one of my connectors that was intermittently shorting out against the case and opening from the pin. Top that off with a short on the other end inside the Motor IC box. Basically my soldering skills need improvement.

[dracozny]

Spent more time on the mill yesterday. after removing the head I ground away the rough channel that was poorly cut by the factory. it took about a day and a half because the smaller Ryobi grinder I was using burnt out it's switch shortly after starting and the larger century tools grinder was just a menace to use, plus the cutting wheel was just so worn out to make any depth.

After installing the ball screw, and moving the head up and down I started to see if I could calibrate the motor without using a gas spring. Unfortunately the Gib was still too loose and slipped tight, I wound up breaking the bolt holding the ball screw mount to the Z axis. so I learned two things as a result, if you do not make a little circular nub on the end of the mount to insert into the Axis then you need to make a spacer to fill that hole, or the bolt will bend and eventually break. The other thing is I had tightened the screw as tight as it would go to prevent the Gib issue but it just would not budge by hand. So I yanked out the cordless drill on low speed with a flat blade driver and very carefully cranked away on that screw. played with the sliding by hand if it bound up at all I gave another turn or so with the drill. It was a bit nerve racking considering how tight this screw was acting.

At this point I moved the motor up and down by hand and with my cordless drill to see how much torque was going to be needed to move it up. I wasn't too thrilled by this and I had already ordered a couple 150lb gas springs. I only used one on the right side but after installing it I realized I should have spent more time looking over the column because the crank mounting hole sticks out too far. So I had to carefully pull the ball stud from the gas spring and slide it over using some scrap aluminium then yank out the Old Grinder and carefully shape away the offending protrusion. I was annoyed by this because I had to spend more time cleaning away grinding dust which is a major nuisance, it likes to stick to everything.


Now to remove the spindle feed and Igaging stuff.

[dracozny]

Finished up my Ball screw mounts today. I had some strange troubles with my Z axis randomly diving down during my cutting operations though. A bit of a nuisance. Accuracy wise I kept everything close enough despite the gouging. I made the Y ball nut mount into an L shape in order to clear the underside of the base. not sure how I am going to resolve the issue. it seems large moves on the Z are fine but smaller moves tend to be a bit random. I am sure some of that is due to backlash and more of it to do with lead error. but why the system is dropping I find confusing. If I cycle the axis up and then back down it's positioned correctly again.
One thought is to throw more hardware into the equation, adding another mesa card to support linear encoders along with the rotary encoders would probably be the ideal solution but my electronics cabinet is plenty stuffed already. On top of that is the lack of funds of course.

[ninefinger]

Linear encoders won't help with the sudden droop. I have the same problem with Z gouging. Its the Z slide slipping / sticking coupled with (in my case) a single ballnut on the z( few thou backlash) and the top angular contact bearing block / bearings being crap (from Chai) having slop as well.
I haven't come up with a good solution so far, for small light duty stuff (1/4" endmill or less) I set the gibbs looser so the head doesn't pull down as soon as you start cutting.
For heavy cuts I whack the head down before it engages the part - neither is good for an automated cut or in a pocket.
Not sure if a counterbalance setup would help with the stick - slip if it was positioned so that the head was properly balanced and not cantilevered off the column? Looking forward to see if you have a solution that works (and is cheap)
Mike

[dracozny]

Linear encoders won't help with the sudden droop. I have the same problem with Z gouging. Its the Z slide slipping / sticking coupled with (in my case) a single ballnut on the z( few thou backlash) and the top angular contact bearing block / bearings being crap (from Chai) having slop as well.
I haven't come up with a good solution so far, for small light duty stuff (1/4" endmill or less) I set the gibbs looser so the head doesn't pull down as soon as you start cutting.
For heavy cuts I whack the head down before it engages the part - neither is good for an automated cut or in a pocket.
Not sure if a counterbalance setup would help with the stick - slip if it was positioned so that the head was properly balanced and not cantilevered off the column? Looking forward to see if you have a solution that works (and is cheap)
Mike

Well I made my own bearing blocks since I read early on that the one chai provides are crap. plus I have double nut ball screws so the play should be non existent especially since I rebuilt the spacers with my own combined with two bellville springs.

I did discover what was happening though. My backlash was horrendous given everything I mentioned and I discovered before pulling the head that the bolt holding the nut to the Slide was loose. I actually could watch it wiggle as I spun the screw back and forth. It was causing around .08" of backlash. After torquing it down my back lash is now .007". It's still more than I would like but it is much more responsive now. Not sure what I can do to remove that .007" at this point. it's possible that I may not have enough preload on my spacer like I thought.

[arizonavideo]

The head dovetails are notorious for rocking on the 45's, if you place an indicator to look for rock I bet you get a couple thow right their.

[VitaminD]

Arizona video is right however there is a fix for this issue.also were are you getting back lash

[dracozny]

with the gibs locked down I get backlash at the pulley even after torquing down all of the bolts. either the slide is flexing or my mount that I made is flexing, possibly a combination thereof. It's a double nut ball screw and I completely replaced the spacer so I know that should not be a factor. after I finish the y motor mount I will look into it further.

[ninefinger]

What do you mean "backlash at the pulley"? Is it rotational backlash ie turns a few degrees before it moves? Have you checked the ballscrew shaft for movement under load (moves up / down when you apply a load)?

[dracozny]

What do you mean "backlash at the pulley"? Is it rotational backlash ie turns a few degrees before it moves? Have you checked the ballscrew shaft for movement under load (moves up / down when you apply a load)?

yea the shaft turns about 3 teeth from one extreme to the other with the gib locked down and about 80lbs of torque applied to the pulley. The ball screw does not move longitudinally my bearing mounts and preload are solid. As mentioned either my ball nut mount is warping or the slide is flexing.

[109jb]

80 pounds of torque? If you mean 80 inch pounds that would equate to 1280 oz-in and about 2300 pounds of axial screw force for a 5mm lead ball screw. I would not call it backlash with the gibs locked down. Backlash should be measured with properly adjusted gibs using a dial indicator to determine the backlash.

[dracozny]

80 pounds of torque? If you mean 80 inch pounds that would equate to 1280 oz-in and about 2300 pounds of axial screw force for a 5mm lead ball screw. I would not call it backlash with the gibs locked down. Backlash should be measured with properly adjusted gibs using a dial indicator to determine the backlash.

To clarify we have already adjusted the gibs properly with a dial indicator. We are trying to identify other causes of backlash at this point. lubrication is also ruled out.

[arizonavideo]

Have you checked the Gib for contact area?

Many are machined at the wrong angle so the slide will rock rather than move.

If the slide is locked and you can turn the pulley 3 teeth then I would look at the ball nut itself. For the Z it is hard to have more preload then the weight of the head so backlash is a problem.

[Roadstercycle]

Hi Drac, I just noticed your Z problem. OK, here's how you can determine wether its the ball nut, or the ball nut mount bending. Lock your Z-axis, turn the z screw by hand, if you get backlash then it's the ball nut since you are not using any torque just hand pressure and you have already eliminated the possibility of your end bearing having any slop, make sure your z-motor is unplugged. If you do not get backlash by hand then you move onto your z-axis ball nut mount. If you think that is it then double check your dimensions of course you know that already. You can also remove the alignment pins if you used them and drill and tap those holes too in your z block, that will give you the main center bolt and 2 extra bolts for holding it solid. Actually I don't even know if on your machine you have the 2 extra alignment pins. I'm sure a lot of us would like to be there to help you out but we can't, so just throwing thoughts out there. Hope you find it.

[dracozny]

yea I don't recall any alignment pin. the original acme nut. just had a slight protrusion that inserts into the slide and the large M8 bolt threads into that from the slide face.

I can turn the pulley by hand, although it takes some effort. I need to get some sort of gauge in there to figure out what specifically is moving.

[Roadstercycle]

I was not sure if you had them or not, my I.H. had 2 that I just used there holes as a drill guide after I torqued the main bolt and aligned the shaft. I don't know if you the Chinese anti backlash screws and nuts but I seem to have some back lash in my X axis and I think it's the ball nut. Bummer.