[archistrong]

I know. I know. There are a ton of G0704 builds on here, some are incredibly well done! I thought I'd share my build as I'm coming at this from the standpoint of having absolutely zero background in the practice of machining. I've always been fascinated by the dark art of the Machinist but I always felt it was outside my abilities. I'm trained as an architect so I work with ideal situations and abstract concepts all day. The practicalities and realities of machining are very interesting and new to me. I picked up a G0704 mill last August (2013) but between a move to a new house, a new job and a 2 year old I'm just now getting to the build. Below are some shots of the small sliver of space I have carved out for my "shop" (don't laugh).
Attachment 244892
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I have been using the mill off and on for the past year and it definitely worked out of the box but the finish and accuracy was all over the map. The Z axis was very hard to crank and would stick at certain points. I could never get the head trimmed properly, there were just some weird geometries going on. Enough is enough, it's time to tear down and see what shape things are in. Disassembly of the x and y axis was straight forward and I potted with Prussian blue on my surface plate. Yikes...

Y Axis on the saddle.
Attachment 244904
Y Axis Gib, only a few points of contact.
Attachment 244902
X Axis on the saddle appears to be warped.
Attachment 244906
X Axis Gib
Attachment 244908
Table ways, these were rediculous! I need to order a larger surface plate (only have a 12x18) to do a proper spotting and measurement but first glance shows that on one side there is only a 1" x 1/8" zone of contact! On the other side there is a very thin knife edge that is running down the table.
Attachment 244910
At the very end of the table bearing surface there is a 1/2" patch of raw casting. This won't ever impact the function of the machine but is still representative of the quality of the castings.
Attachment 244912
The ways on the bed looked like the teeth of a file. These surfaces were not ground, just raw milled and left "gud 'nuf". Like I said, I'm no expert in these machines but I'm pretty sure that this surface shouldn't double as a nail file.
Attachment 244914
The gib bearing surface on the bed has serious gouges in it.
Attachment 244916
In fact, the only things that were "scraped" were the gibs and the Z saddle / head surface. The Z column has the same nail file finish.
Attachment 244918

I have a lot of scraping in my future to say the least. I will tackle this in little bites as time permits. Bear with me as I'm sure to have questions and this is going to take some time. The next couple of steps I want to tackle in their week or two are:

-Measure for any warp / twist in the ways.
-Mill / scrape a dovetail straight edge.

You will probably see techniques borrowed from Hoss and Ryan's G0704 builds (and others) so I will try to make sure I give credit and link to resources when I can. The build will come in phases from basic to more advanced as I become more familiar with the techniques and technologies involved (not to mention cash and time).

Thanks and stay tuned!

[archistrong]

I'm curious to know if anyone else's G0704 has similar shoddy machining of the ways. I'm perfectly fine trying to scrape the saddles and gibs as they have already been properly ground and at least had an attempt at scraping done at the factory (albeit fairly poorly done). I'm actually looking forward to it. However I'm not sure that it will be possible to scrape down bearing surfaces that have the rough machining marks still on them. The Z Column and Bed ways are so rough that it sounds like driving down a washboard road when sliding the saddles by hand. The dovetail on the Z Column also looks to have been improperly machined (similar to what Zach saw during his build) I've gotten in touch with Grizzly about a warranty on these castings and they said that the guy who deals with these machines is out till Tuesday. Guess we'll see what he says.

I've been spending the past year modeling the machine in Inventor (based on an existing CAD model from Benchtop Precision) and have started to modify parts based on the different phases I'd like to progress in. Since I don't have access to a CNC mill in town, everything will either need to be simple 2D machining or 3D printed parts (we do have one of those in house!). The printed parts are based on Hoss's designs and adapted for my own specific needs. Right now I'm planning to use 570 oz/in NEMA 23's on the X / Y and 906 oz/in NEMA 34 on the Z.

Attachment 245032

X Axis Motor Mount
Attachment 245038

Y Axis Motor Mount
Attachment 245036

Z Axis Motor Mount
Attachment 245034
I'm also working on bringing jmillerid's X/Y saddle oiling manifold into Inventor. There are some pretty awesome tools in this software package, including piping and wiring runs. Makes design of these objects pretty quick. Still need to work through the best way to bend such small diameter tubing. He has a nice writeup on his blog about how he went about bending tubing for his build but I'd like to try and get tighter bends if possible.

Attachment 245030

Also thought I'd share a quick project I finished up a couple weeks ago. I needed to rebuild the Holley carb on the Corvette I've been restoring and liked the idea of having a carb stand to make adjustments and cleaning easier but I didn't like the idea of paying $50 for one (I can be really cheap about some things). I designed this piece in Inventor and then printed it out on our little MendelMax 3D printer. Added a few bolts for studs and you've got a simple, dual function carb stand!

[gcofieldd]

I like where you are headed and all the modeling. I looked at mounting my y-axis the same way you are but when I moved the table forward and all the way to the left the end plate hit the stepper motor, do you have that issue?

[archistrong]

I agree, I took this approach as I've not liked the idea of having the Y axis motor hanging out so far. I've got such limited space to work in that I'd be bumping into it every time I walked past and since I'm planning on printing it there is a good chance that I could just snap it off! The first version of the mount had that same problem of running into the X table so the second version aligns the motor with the angle of the bed and adds belt tension adjustment along that axis. This should be enough to keep the table clear of the motor.

Attachment 245048

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I do have a clearance issue with the mounting bolt at the front right of the bed but I think I can just mill down the head of the bolt to get the clearance I need. Here's a picture of just the mount itself

Attachment 245054

I can upload a copy a STEP model of the mount if you'd like to play around with it. I add the caveat that I haven't tested it yet in the real world.

[Wiggles84]

The area on the underside of the table that you have bluing on is just clearance. If you look at the area of the saddle wear it would contact, you'll see that that area isn't finished either.


Just wanted to get that out there before you put a ton of work into an area that will give you no return.

Andrew

[archistrong]

Good point, I didn't catch that!

I'm not sure which is worse. The nail file finish or the apparent warped table. I'll have to check overall table flatness as I don't have a straight edge to spot the ways on the table. I'll get back to ya on that one.

--Edit-- the ways on the table are incredibly rough. Can't believe that the bottom of the table is ground but the actual ways are rougher than some of my files.

Attachment 245056

Also spotted the table. Definitely appears to have a twist in it.

[archistrong]

Decided to have a little fun tonight. I wanted to run a basic stress test of the castings to see how they react to typical milling stresses. I had a hard time finding any documentation (that I could understand at least) which gave me an idea of the forces involved in a given milling operation. My guess is that there are so many variables that its almost impossible to come up with a single formula for all scenarios. So I setup some basic constraints. I am assuming that a climb milling operation @ .25" depth of cut, .25" width of cut using a .5" 2 flute endmill, 2200 RPM @ 250 SFM (from right to left) would produce roughly 100lbs of force in roughly a 45 degree direction from the center of the cutter. In the end I got some pretty interesting results (note: deflection is shown exaggerated from actual results).

Attachment 245084

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Spindle deflection topped out at .0017" and table deflection topped out at .00019". I was surprised to see just how much spindle deflection there was. I really have no frame of reference to know whether or not my assumption of loads is correct or not. So take these results with a grain of salt. Regardless, it is interesting to see how the column deflects and gives a frame of reference for trying to add stabilizing compenents to restrict movement of the column.

[embraced]

How did you calculate the force required to make that cut?

[CRO-WD40]

My guess is that there are so many variables that its almost impossible to come up with a single formula for all scenarios.

There's always worst case scenario.

Power available at lowest possible RPM , gives you torque on the spindle. That torque on the smallest possible endmill that can transmit that cutting force without breaking gives you the force that the machine will see. It usualy ends up in some awkward machining parameters, but it uses all of the available motor power.

- - - Updated - - -

How did you calculate the force required to make that cut?

download sandvik endmill catalogue or some other manufacturer, you got all formula's inside.

[archistrong]

Thanks, good idea! I had a look through the sandvik catalogue which had some great stuff in it. Still couldn't come up with a formula for milling force (maybe I'm just dense). I did find a formula which I think will work here:

Attachment 245102

Knowing the max horsepower we can get from our machines is 1HP (at least in stock form) and recommended SFM for steel using a HSS endmill is 70 the formula reads as:

(1HP x 75% x 33,000)/70 = 353 lbs

This chart from G Wizard shows vectors of forces from different milling actions:



I'll update with this new force and I need to add a torque force to the head / Z saddle joint which is missing right now.

Does this sound right?

[SCzEngrgGroup]

Torque is simply force times distance. If you have a 1/2" diameter tool the distance is 0.25". If you then have a torque of 1 ft-lb, or 12 in-lb, then the force applied by the tool is 12 in-lb / 0.25 in. = 48 pounds. Of course, with a real tool, it's more complicated than this, but this is a perfectly reasonable approximation for modeling purposes. If the actual torque is not known, it can be calculated based on the work done, which can be calculated based on MRR and the material being cut. There are numerous on-line calculators for all of this.

Regards,
Ray L.

[archistrong]

Been thinking about the simulation model today and decided to model the bearings / spindle / tool holder / endmill to add to the simulation so that I can get the proper forces applied to the correct faces of the castings. I like these results a bit better as I feel that they more accurately model the conditions happening on the machine. The forces were used based on the calculations I made this morning and applied to the model. My assumptions this go around were:

1/2" Endmill, .25" DOC, Slot cut, 70 SFM

Disclaimer - I'm an architect and my understanding of engineering concepts is rudimentary at best. Sorry if I have butchered these simulations.

Came up with some interesting results. Max deflections were as follows:

Endmill: .0044"
Head Casting: .0034"
Column: .0011"
Table: .0001"

Stress Model
Attachment 245156

Displacement Model
Attachment 245158

This condition would more than likely result in some serious chatter and may even break the end mill or stall out the machine. It's as close to a worst case scenario I could come up with.

What is interesting to see is the strain graphics for the head and column. The head casting is interesting just to see all the forces working their way through all the complex geometry but the column is interesting to see where the stresses are concentrated so that we can add reinforcements to those areas. Right now I'm toying with the idea of adding steel plates bolted to three sides and an EG (epoxy granite) casting around the outside of the column to add damping mass. I tried plowing through the EG forum last month and probably only made it through a quarter of that thread before I was entirely lost.

Column Stress Model
Attachment 245160

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Head Stress Model
Attachment 245164

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[bjones]

i don't see the point of doing these tests as you are completely guessing at the data for the forces involved, as you've said yourself you have no experience at all. the figures you keep giving as results are pretty useless.

[archistrong]

i don't see the point of doing these tests as you are completely guessing at the data for the forces involved, as you've said yourself you have no experience at all. the figures you keep giving as results are pretty useless.

While I agree with you that I don't have extensive experience with FEM modeling, I do understand the basic principles. The assumptions were not guesses on my part but were based on information found on the sites I linked to above by myself and others. I'm not trying to create a comprehensive study, just trying to see where the weak points are in the machine.

The deflection numbers may not be that important by themselves but they act as a baseline for anything I try to do to stiffen the column in the future. Same goes for the stress locations in the column. I'd rather know before I go through the effort of stiffening the column that it is going to have the desired effect. If I can reduce deflection by half I figure it's a valid test.

In any case, just my personal experience from using the machine tells me that the column could be improved to some degree by stiffening it. I can impart noticeable deflection just by pushing on the column by hand.

What have people tried here? I know I've seen a couple builds where people have added either steel or granite gussets to the column, I'd be curious to know if that approach has worked for them.

Thanks!

[TroyO]

I was faced with scraping that table and a lack of sufficient surface plate for the job myself. I ended up making a "composite" straight edge with some granite tile glued together with JB weld and trued up with diamond hones. (Referenced to the surface plate by blue-ing it and doing sections.)

"Composite" straight edges?

It wasn't perfect but it was darn close. It didn't flex out of shape during the month or so I needed it and it was dirt cheap, LOL. It wasn't very durable, but I think I just might make another slightly thicker one and treat it better to see if it "holds" long term.

Just food for thought.

[archistrong]

Thanks TroyO! That's an interesting idea and one I might look into. I just got an 18" length of 1x2 cast iron bar in the mail that I'm going to machine down into a dovetail straight edge on the Bridgeport at our office. I don't think I can go any longer because the old Bridgeport is pretty far out of alignment when you get to the extremes of travel (+.004" on left, +.0025" on right). To make something longer for the columns and table I'll look into this further.

How rough were your castings? Did you have the "file" machining texture left on the castings? They are so pronounced on mine that I don't know how effective scraping is going to be. I'm tempted to re-machine the suspect ways with a dovetail endmill. Not much, mind you, only enough to knock down the high ridges so that I can even begin seeing the spotting dye. Right now it's like standing a bunch of knife blades on edge and trying to read the spotting.

[TroyO]

My table and base castings were fine, the saddle was not the best and took several passes to get flat/coplanar but once done it measured out at .0004/12" error..... I'll take that, LOL. I haven't done the column yet, that's in the current work pile.

It's definitley got some "tooth" to it but I doubt it's very deep. You can just barely catch a fingernail in the texture so I'm guessing the tooth is less than .001.
I have not had a chance to check straightness or anything yet, but my guess is that it is straight and reasonably flat it just could have used another couple passes at the grinder. I suspect the dovetail plate and head mating surfaces will need more attention, much like the saddle but again it's just spitballing a guess at this point.

I'm not too displeased with it, but my standard of comparison is a Mini-Mill so maybe my standards are just very low, LOL.

[archistrong]

I haven't been able to make much progress on scraping the ways on the machine as Grizzly decided to warranty the entire mill. What started as a general question to them regarding typical finish quality and also the fact that the Z column dovetail hadn't been fully milled (couldn't move the last upper three inches of travel). I spoke with them last week and, good news, they're going to warranty the entire mill! Oh, and can you crate up the old one to be shipped back?

There's now a big hole where the machine used to be. Not sure when the new one will ship. Guess that gives me more time to do some modeling in the computer.

[Dingus]

I haven't been able to make much progress on scraping the ways on the machine as Grizzly decided to warranty the entire mill. What started as a general question to them regarding typical finish quality and also the fact that the Z column dovetail hadn't been fully milled (couldn't move the last upper three inches of travel). I spoke with them last week and, good news, they're going to warranty the entire mill! Oh, and can you crate up the old one to be shipped back?

There's now a big hole where the machine used to be. Not sure when the new one will ship. Guess that gives me more time to do some modeling in the computer.

Did you ever get your mill back? If so how did the ways on the new one look?

Im dealing with Grizzly tech support on mine right now and wondering if I should just return it since I am within the 30 day window or trust that a replacement from Grizzly will be better.

See this thread if you are interested in my experience:
http://www.cnczone.com/forums/bencht...79968-cnc.html

[archistrong]

It's been a while since updating here but Grizzly was pretty attentive about the whole process. I was expecting to have to jump through a bunch of hoops but after crating up and shipping it back they had a new one shipped out in less than a week. In the end they warrantied the mill because of the defects on the Z Column (dovetails not fully machined). Frankly, they could care less about the rough "bastard file" like finish of the ways, chalking it up to the face that these are "not professional machines".

The new one I received has the full range of travels that it says it should. After taking some initial measurements of the accuracy I tore it down to check alignments. I'm not sure how much scraping I'm going to take on as I only want to do it once and do it right. I figured I'd get my eye in by scraping the base of the machine flat. I have a surface plate (B Grade) from Shars which arrived damaged (one corner broken) and they let me keep it rather than sending it back. I plan on coring holes through the granite plate and mounting the mill to this as part of the machine base. I put the base upside down on the Bridgeport here at the office and used a Tormach fly cutter as a starting point. In general, the scraping process went pretty smoothly, though I would definitely use a carbide scraper. I started using a steel scraper but it never cut consistently and always left scratches. You can see the progress here:

Attachment 257664

I've since switched to a Sandvik Coromant scraper I picked up off of eBay for cheap and its a night and day difference! Easier to cut, smoother finish and easier to control. Once I finish it up (after the Kitchen Reno is done) I'll post some additional pictures.