[tjschweizer]

Hello everyone and welcome to yet another G0704 CNC Conversion thread. Brace yourselves for a wall of text, I've been prepping for this for 3 years now...

This has been a long time coming, I first purchased a G0704 back in 2012 and had to get rid of it in 2013 due to some financial issues - little tip: don't try to build a CNC mill living in a college dorm room. Anyways I got another one a few months ago and now I am living in a nice roomy house with plenty of space for a CNC mill, and a higher paying job so fingers crossed! Although I am still attending college.. Also I'd like to mention I am keeping all of this logged on my website with more pictures and videos, so if it seems like I haven't updated this post I might have updated the site - G0704 CNC Conversion | Learn CNC . Shameless promotion for my site, I'm working on making a bunch of informational videos on building a CNC mill.

To start off I'd like to throw some acknowledgements: first is hossmachine and the insane amount of information he provides both on the forums and his DVD which I purchased way back in 2012. Second is Ryan's G0704 build thread - I learned a lot reading his thread and he really showed what is possible with these machines, just a lot of great info in that thread. Third is the recent thread about a G0704 Linear Rail Conversion which BTP converted the Z axis to linear rails - more on that in a minute. Finally a shoutout to everyone on this forum posting build threads and comments, there's enough info on this site to last a lifetime. Alright now for the exciting stuff.

This won't be a typical run-of-the-mill conversion - the main "feature" I am focusing on is removing all of the dovetail ways from the G0704 and replacing them with linear guides from Misumi. There were several reasons I decided to do this, but the biggest one is because I simply haven't seen it done before. But there are some actual reasons, largely the inaccuracies in the stock dovetail ways. In Ryan's G0704 thread he scraped all the surfaces, which I actually planned on doing - I even bought a surface plate and made some scrapers - or I could've just lapped the ways, but I figured the time I'd spend scraping or the money I'd spend on encoders to compensate for geometry errors in the lapped ways I might as well just use some linear guides.

The first step was to model all of this in Solidworks. A cnczone user onocyclone had made a Solidworks model of the AMA25LV which you can find on grabcad, but after checking the dimensions to my mill they were slightly off. I figured this was probably due to different years of manufacture. So I started modelling everything besides the head since I plan to replace the spindle with a geared down VFD with an ATC and... I'm getting ahead of myself. Anyways I used onocyclones head model, but made the rest for my mill. I plan on making my CAD model available, minus any parts that were not designed by me - for instance I purchased ballscrews according to Hossmachine's dimensions, so I won't be posting the models of those.


I started working on the Y axis, adding in the linear rails, bearing mounts, motor mounts etc. I made the mistake of buying the ballscrews before I had everything planned out (linearmotionbearings on eBay), so I had to work around some dimensions. I'm going with a servo motor from Teknic with a 3:1 belt reduction. I haven't completely settled on Teknic, I'm bouncing between them and DMM-Tech. I really like the idea of Teknic's integrated servo driver, but the torque specs aren't quite as good. Anyways I will be buying my pulleys from Misumi - this is because of the ballscrew dimensions I am working around, usually I would get them from sdp-si.com but I needed a style that they didn't offer and Misumi did. Similar price. GT2 2mm pitch 9mm belt width. The linear rails are the SE2BD16 rails, for the Y axis with the spacer from Hossmachine's plans a 390mm rail fits perfectly. They custom machine them to any length you want for like $13 extra, but 390mm works perfect. They are a 15mm wide rail, with a 16mm clearance form bottom of rail to top of cart. The SE2BD16 series is dust proof with a seal for stopping chips from getting in the cart bearings, and has a slight preload in the bearings. For one 390mm rail with 2 matched carts it is $130, making $260 for the Y axis.



For my ballscrews I will be using a double ballnut setup, with a wave spring washer from Mcmaster Carr. I have my Solidworks model setup with a spring configuration that should let me have a spring preload between 10-50 lbs, which I can adjust with shims. I will be using angular contact bearings from Misumi - usually I'd use VXB but Misumi is around the same price and might as well combine orders. Here is a picture of the setup, the small pieces between the right ballnut and the mount are the springs.

Once I got to editing the saddle and realizing just how much work needed to be done to it, I realized it'd be much easier to just make one from scratch. I will be making it from 1018 steel, it will be roughly 7"x7"x1" thick. This should be more rigid than the stock saddle, in theory. The X axis is similar to the Y axis, except I had to modify the ballnut setup. I will be using a large spacer and springs to get the same effect though. You can see the bottom of one of the ballnuts against the saddle in the next picture.

Here is a better image of the saddle.

And one of the X Axis motor


And the same thing applies to the Z axis, although the mounts don't look pretty they do the job. I will be able to adjust the preload of the AC bearings on each ballscrew with some shims.

And finally a full model


So now moving forward, I will be finishing up the model and adding all of my bolts/fasteners/shims etc. to make sure I won't run into any issues. Then I will be planning out how I will modify the stock castings to fit everything. I will probably be doing this axis by axis, get the Y axis finished with the rails and bearings and everything then start the X then the Z and so on.

Some future plans are a 4th and 5th axis - I have some ideas on how to eliminate vibration in a rotary axis, you can view my post history to learn more. I want to build an ATC and include a touch probe for setting my coordinate offset and a tool probe for tool length offsets. Right now I have access to my university's MasterCAM with multi-axis capability so I'd like to play with that a bit. I'm also planning on a coolant and oiling system, and I found a way to make super cheap linear encoders that I actually hope I can turn into a marketable product. Lots of things on the to-do list. I'll update this thread and my website as often as I can, I'm hoping to get as much as possible done before classes start so it should be an eventful couple weeks.

[AVRnj]

Looks like a pretty exciting build, looking forward to following along.

[rowbare]

I like the idea of discarding the original saddle and making your own. I suggest you pocket the saddle for the blocks. It will reduce the distance between the axes and make it a bit more rigid.

bob

[tjschweizer]

AVRnj-
Thanks, did you find the rails?

Rowbare-

I would, but I am already struggling to fit the ballscrews under the table. Great idea though, I'll try playing around with the dimensions to see if I can get it to fit better.

[AVRnj]

I did, thanks.

[BTP]

Ball screw clearance is a problem with these machines on the x&y for sure. I'm glad my Z axis mod was some inspiration for you. That's what it's all about, share your ideas and projects with other people and see what stems from it.

I also plan to do the x&y linear rails myself. Interested to see your project progress.

[sbeckett]

Nice work. Here is what I have been imagining might be fun to construct. Target travels are X = 12.00 inches, Y = 9.50 inches, Z = 12.50 inches.
Attachment 289344

[lcvette]

Do yourself a favor, instead of using a spacer on the back between the base and the column and having to use foot long bolts, put the spacer in the front and motor in the back... You'll thank me later!

It will be much more solid with shorter bolts and the joint connected against the the base. The spacer in the front won't be seeing direct vertical cutting loads because the spindle centerline will still be over the main base so all of your connection points are more rigidly connected.

You will have to notch the front of the base for the ball nut and screw, but you will be reinforcing it with the steel spacer block bolted to the front. You can also use the spacer as a bearing support for the ballscrew. That is how I have my linear rail conversion designed. Just waiting for some time to start it.

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[tjschweizer]

sbeckett,

That looks like a very rigid machine. Based off of a G0704 right? I really like your idea of leaving the table moving on the Y axis and making another table for the X. You gain a lot of rigidity that way. I might try that.

lcvette,

I can't believe I didn't think of that! Great idea. I will definitely be doing this. Now I've got to rework some of my Solidworks models.


General update:
I found out Misumi gives students a 30% discount, so anybody who is a college student just let them know and you get 30% off. Great deal.

[sbeckett]

sbeckett,

That looks like a very rigid machine. Based off of a G0704 right? I really like your idea of leaving the table moving on the Y axis and making another table for the X. You gain a lot of rigidity that way. I might try that.

Yes, G0704. The table the X Axis moves on is the original with some modifications. I was thinking about filling in the slots with a particulate filled epoxy to help stiffen it up a bit.

lcvette - I am still thinking about how to keep from using long bolts to go through the column / spacer and into the base. Still have a lot of work to do on other stuff first.

[lcvette]

Just remove the rear spacer and extend the front spacer.

Also flip the table back over, you'll have more Y travel and x travel, 2 bearing trucks on the Y slide is plenty for our little table and it eliminates the ballscrew being exposed. With the linear rails it won't bind fully extended even with weight on it... It will be super smooth.

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[tjschweizer]

I don't think I can do the spacer in front, I don't quite have the necessary ballscrew length unless I do a direct drive. I might be using steppers instead of servos temporarily (until I can afford the servos), so a direct drive might be possible. Although if I were to make the brackets for a belt drive, once I did upgrade to servos it would be a simple plug and play.

[rowbare]

I don't think I can do the spacer in front, I don't quite have the necessary ballscrew length unless I do a direct drive. I might be using steppers instead of servos temporarily (until I can afford the servos), so a direct drive might be possible. Although if I were to make the brackets for a belt drive, once I did upgrade to servos it would be a simple plug and play.

What if you extend the spacer to the side and pocket it for the belt drive thereby combining the motor mount and the spacer? That would leave you with a nice compact setup with the belt drive out of harm's way.

bob

[lcvette]

I don't think I can do the spacer in front, I don't quite have the necessary ballscrew length unless I do a direct drive. I might be using steppers instead of servos temporarily (until I can afford the servos), so a direct drive might be possible. Although if I were to make the brackets for a belt drive, once I did upgrade to servos it would be a simple plug and play.

You can always order a longer screw. You already have the ballnut for it, pretty cheap in the grand scheme of things for a more rigid machine... Motor in the back is the only way to go in my opinion, reduces cables in the milling area, keeps the motor dry and away from chips/coolant, cleans everything up and gives you better front clearance for loading and unloading parts or training or anything really.

At this stage of your design/build making changes to improve rigidity is easy, when its completed is when the change is a problem. Get a longer screw and don't compromise the better design, I have done it the other way and can tell you. The longer bolts and spacer don't help the column flex issue. I actually fastened my enclosure walls to the column and with the spacer in the back. If I have a indicator setup for training and lean on the enclosure I can get about .005-6" deflection because the column is not as stable. It was far more rigid when stock and bolted to the base directly and my surface finish was superior to what it was with the spacer. These little machines can make nice parts, but when you start extending things to get more travel, the quality and tolerance falls off a cliff.

You are already addressing one of the biggest issues by going to linear ways, but keeping the actual structure rigid is every bit as important. Eliminating play from the dovetails and keeping it rigid by minimizing deflection from cantilevering the column so far out will be about the best this little machine can do. Especially since you are also hanging the heavy spindle head further away from the column.

I have a design for my conversion that actually uses a custom fabricated steel stand that goes about 2 feet past the base in the back and will use bracing to tie the column top and midpoint to the base and stand with triangulated and webbed bracing. I have a plasma machine and Welders and a full fabrication shop so while not cost effective to most. For me that is cheaper then starting with another mill (which I am still considering though).

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[tjschweizer]

rowbare:

Do you mean with the spacer in front? Having the motor and spacer in front? That... actually might work. Thanks!

lcvette:

I agree about getting a longer ballscrew, it would definitely make things easier. Now that I found out Misumi gives a discount for students I might just get a ballscrew from them depending on the cost. Keep in mind I only work part-time, so cost is a pretty big factor in my decisions. Have you tried using separate bolts for the spacer and column? For instance drill and tap four holes into the base, bolt the spacer to the base with those holes and use the original holes for the column. Still not as rigid as no spacer, but it should be better.

[rowbare]

Yes, put the spacer in front and build your motor mount/belt drive into it. It will be more than strong enough.

bob

[tjschweizer]

So I have been pretty busy lately, but I finally got around to messing with my model a bit more. So far I've probably got 60 hours invested in this CAD model... So many revisions, changes etc. Plus our school just upgraded to Solidworks 2015 so I've been playing with all the new features, mainly replacing my hole wizard holes in the individual part files with hole series in the assembly - this way I can modify my holes faster and easier. Anyways here is my progress so far. I moved the Y spacer to the front. This worked wonderfully. I won't even have to add clearance to the Z axis column for the ballscrew, it doesn't stick out at all past the base. I also added stepper motors to the model since I will be using steppers temporarily - once I upgrade to servos I'll just use the steppers for one of my future projects. And I started working on how I was going to make my X axis ballnut spring-loaded. I came up with a design that I think should work, check out the pictures and let me know what you think. I decided to make mounts for the ballnuts that will bolt to the saddle, this way I can accurately machine the mounting holes for bolting the ballnut to and I don't need a 2" thick piece of steel plate... Finally I will be ordering my linear rails tonight, and they should be here before September. So for the next few weeks I'll keep working on my CAD model and start machining the stock pieces.

Attachment 289754

Attachment 289758

Attachment 289760

[lcvette]

Much better looking design. Couple things I see....

1- still preferable to get the motor in the rear, especially if you will run flood coolant which makes a big improvement in both cutting speeds and finish quality.

However if you are dead set on having it in the front, make sure to notch the motor plate to match the linear rail cutouts on the mill base. As it sits if you get any swarf build up it has no place to be evacuated between the rail and base. Even if you use a way cover it won't keep all of the swarf off especially if you have a fog buster or flood coolant in an enclosure it tends to get everywhere especially with larger longer running jobs.

2- you may want to consider a little more extension on that front spacer. If you haven't considered it yet, you can swivel the head of the mill 90° and use it as a cnc lathe. I found this to be a very convenient setup to have 2 machines in one. With a little extra Y travel you can setup some very neat gang type tooling for zipping through turning jobs with a single setup.

Just food for thought and hind sight from my previous builds!

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[gd.marsh]

All you will need to do is fab a cover for the motor & pulleys and you won't have problems with flood coolant .. I've been running my mill with pretty high pressure coolant for nearly 5yrs now with the Y axis motor hanging right out in front & covered.

Yes, chips & coolant do get flung everywhere in the enclosure, but I haven't had a single problem with electrical since I covered my motors & ran all motor wires through flexible conduit with liquid tight couplings at both ends.
I've found that automotive heater hose works well for this. Flexible, resistant to chemicals, & cheap. I used liquid tight couplings which took a little fitting, but very doable.

Also don't forget that extra table travel to the front does not all equate to usable table space for cutting, unless you put a spacer behind the head to move it out from the column also. In most milling situations once the table is entirely out in front of the spindle, you loose sufficient support for milling. If you hang a fixture off the back edge of the table to support your work, it will hit the column before your tool reaches the front edge .. Adding a spacer behind the head to move the spindle more generally to the center of table travel will give you greater usable travel, but you'll run into flex problems with the column unless you stiffen it somehow to combat it ..

Going to be a great build .. I'm watching with great interest!

gd.marsh

[lcvette]

I have my x covered, and after a 2 week hiadus from being run, I was greeted by it being frozen up.. I tapped the back of the shaft a few times and it freed up but now it makes a nice grinding sound as it works.

Steppers generally don't have nice watertight wire entrances like servos do...

My suggestion was geared towards more travel with the head tilted and an R8 lathe Chuck in the spindle.... No chance of the tool hitting the column before the work piece in that setup. And it gives more options for a gang style tool plate bolted across the far right side of the table. It can use a lot of the extra travel especially when a turning tool is hung away from its mounting point for OD turning.

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