[jviss]

I hesitate to start yet another vanity G0704 build thread, as there are so many great ones here already, and I can only aspire to the heights that others have achieved.

I have ordere the mill, and should have it by the end of the week.

I've ordered a DBTools motor mount kit, plus CJA Masterworks ballscrews and ballnuts, which I think are Roton, from a third part via eBay.

And that's it so far. I have a pretty good home shop, with a Clausing toolroom lathe, surface grinder, horizontal bandsaw, etc., plus a nice measuring bench including a large lab grade surface plate, height gauge, etc. I have reasonable home metal shop skills.

What I would like to do in this thread, at least in "phase one," is have a discussion of the selection of components for the CNC mill. There's an enormous wealth of knowledge on this board, and a lot of interest in this mill and CNC conversions, so I'm confident I'll get great advice on these topics.

So, let's start, if you don't mind, with motors. I briefly looked into servo motors, but it looked like for equivalent torque they were four to five times the price of steppers.

So, what steppers? The X and Y mounts I have take NEMA 23's, the Z NEMA 34. How strong? Are there any other significant differentiators other than torque? Is name brand important?

Next, of course would be drivers. Same idea - name brand? Output rating?

Thanks,

jv

[amyers]

do yourself a favor and check hoss's website, G0704 Electronics he's the g0704 king and has been the inspiration for many of us from the beginning when the g0704 first came out, a huge wealth of knowledge.
am

[Whizbang]

As said above hoss's page is a great place to start.
through his links i found a closed loop stepper setup, I am currently trying to find info about theses as to whether that are as good as servos as you mentioned. If these motors can detected miss steps and correct back lash with the supplied encoder then to me they are just cheaper servo setups.

[DRock]

Did you get BDTools ballnut mounts also with the kit?

[chipslinger69]

BDTools recently had an auction end on Ebay for the motor mounts and ballnut mounts and ballscrew end support bearings. I honestly couldn't see giving that kind of money for the kit but I guess I don't want it that bad.
Grizzly G0704 Mill CNC Conversion Kit Mounts along with Ballnut Mounts | eBay

[jviss]

Did you get BDTools ballnut mounts also with the kit?

There's a long story in answer to that, and the answer is no. At the time of the purchase I was not aware of ballnut mounts. It turns out that the ballnuts I'm getting (haven't received them yet) and made by Roton, and are incompatible with BDTools' ballnut mounts, anyway.



5/8 X .200 Right Hand Recirculating Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

I think it may work out, though, since the Roton ballnuts mount via a threaded portion of the nut, I might be able to make mounts that are very similar to the G0704 stock "half nuts" that have a threaded hole for the Roton nuts instead of the thread for the leadscrew, and of course without the half nut adjustment feature. They would include a set screw to secure the ballnut.

I don't know the dimensions of the X and Y halfnuts yet, but I've already made a 3D model that I can just dimension. Maybe my son can knock them out on a CNC mill at school (he's a PhD candidate in Mechanical Engineering).

For the Z I don't have a design in mind yet. It appears the G0704 does this with two pieces, and BDTools with one.

[Fastest1]

Using the BD Tools kit the way you are will be easy enough. The mounts have very few critical dimensions. Simple blocks and a few holes, pinch bolts do the holding on X & Y. Z isnt much different.

[jviss]

Using the BD Tools kit the way you are will be easy enough. The mounts have very few critical dimensions. Simple blocks and a few holes, pinch bolts do the holding on X & Y. Z isnt much different.

I was following you right up until you said "pinch bolts." I don't know what you mean.

By the way, the machine arrived today; order was finalized Monday afternoon, delivered Thursday around 1:45. The UPS guy pushed it on a pallet jack all the way to my garage door. Nice! It's a straight, level shot to my basement from the driveway.

[Fastest1]

When you start the disassembly and get the X and Y pulled apart you will see there are 2 pinch bolts for each axis. They are pushing the ballnut mounting block against the pocket milled in the carriage. The Z actually has bolts that pass thru. It is not a technique I would have thought of or used but it does seem to work.

[jviss]

When you start the disassembly and get the X and Y pulled apart you will see there are 2 pinch bolts for each axis. They are pushing the ballnut mounting block against the pocket milled in the carriage. The Z actually has bolts that pass thru. It is not a technique I would have thought of or used but it does seem to work.

Wow, man, I feel so stupid. I'm still not getting it. I even googled "pinch bolt" and still couldn't figure it out.

I am further confuse by your saying that there's a ballnut involved. I think the stock setup is leadscrews and "half-nuts" per the Grizzly manual.

If I interpret you correctly I think you are saying that there are a couple of bolts (pinch bolts) clamping the half-nuts to the pockets. I am thinking I would make new blocks that the Roton ballscrews screw in to.

[Fastest1]

You are worrying yourself too much. There are 2 shcs (socket head cap screw) on the carriage facing the Z column and another 2 on the right side of the carriage under the table. These screws are threaded thru the carriage and as they are tightened they push an aluminum block against the other side of the pocket. Pinching it. Technically I think of a pinch bolt as tightening a cylindrical opening. this is the X. See those bolts/screws?

[Fastest1]

This shows both blocks from the top. These are the mounts Billy provides for the 1605 series screws (not Roton). Your mount will attach the same just be threaded instead of a 6 bolt pattern surrounding a bore.

[Fastest1]

This is what Billy's looks like for the Y. I machined that step down in there to gain more Y travel.

[jviss]

This is what Billy's looks like for the Y. I machined that step down in there to gain more Y travel.

O.K., I see. Thanks. Can't wait to take the mill apart and actually get my hands on the pieces.

My BDTools motor brackets and leadscrews arrive today, too.

[jviss]

Has anyone taken an analytical approach to motor selection for this machine?

I confess I knew nothing at all about stepper motors until this week. I read what I think is an excellent paper from Gecko, "Step Motor Basics Guide," available here:

http://www.geckodrive.com/gecko/imag...cs%20Guide.pdf

On the last page a design methodology is presented. This gives rise to a bunch of parameter values that need be specified for the motor selection analysis:

Maximum load (weight) on table.
Load from cutting (is this significant?)
Maximum required speed (IPS).
Required acceleration to max. speed.
Toque to turn the screws for maximum required speed.
Toque to turn the screws for required acceleration to maximum required speed.

Has anyone determined these values for their own design?

Thanks,

jv

[Fastest1]

There have been many threads on this. I do know bigger is not always better. In my past I have typically run the recommended steppers of someone with a successful build that I admired (not 1 particular person necessarily. After tinkering for a few years in it, you come to know a few people's advice as sound. I run 570's on my X & Y and a 960 on the Z. I can run it faster than I will ever need to besides showing off. I can surely break any tool. If you are a highly experienced machinist around VMC's all day, your CNC 0704 won't be fast or impressive. If you are a hobbyist, it will be faster than you can stop it! Easily. Hoss and quite a few others usually have the equation for why they selected the steppers for a particular project. Most of the time Mariss' formulas are quoted or used. It really depends on which part of this challenge intrigues you.

[jviss]

BDTools motor mount kit and CJA Masterworks ballscrew set arrived today. The mounts are beautiful. The ballnuts are as I imagined, the Roton ballscrews with a 15/16-16 UN thread mount.

I was thinking that my plan for a ballnut mount will reduce table travel somewhat. So, a question: what is the hard limit on table travel on the G0704? Is it the halfnut running into the slot for Y, and running into the end plate for X?

Thanks,

jv

[Fastest1]

Yes and yes. I hollowed out the center of my mill as did many others after Hoss' lead. Prior to the mod, collisions with the column were not possible. Until I put a spacer in there I can hit it all day. There is an inch or more travel right there.

[jviss]

O.K., another week or two of thinking and researching for this project leads me here: closed loop operation.

Closed loop operation, i.e., steppers driving the axes, with linear encoders providing feedback on position, has a a lot of appeal. While I have an idea of the various drive technologies, and a vague idea of the encoder technologies, I'm not clear on closing the loop.

First, will Mach3 close the loop? It provides for the connection of linear scales, and will output the readings as DRO displays, but will it actually reference the encoder inputs for real time positioning info, and, for example, disregard step count in favor of encoder feedback?

Or, is the loop closed in the motor controller? If so, can someone point me towards a controller that has this feature? I believe the K-Flop board will do this, but I'm not quite clear on that yet.

In addition, does anyone make analog to digital interfaces for encoders that output analog, i.e., sinusoidal quadrature signals, to convert them to digital for input to Mach3, or other systems requiring digital signals?

Thanks,

jv

[rowbare]

Mach won't close the loop in software. LinuxCNC can, as can Dynomotion and several other controllers.

I think servos might be overkill for this. You can get great performance from steppers. Tormach has some really good whitepapers on their site that explain how they came about many of the decisions they made regarding their machine designs. This paper talks about how they chose the motors and drives for their Series 3 upgrades. It's a good read and very informative.

Direct Document and Software Download | Tormach LLC | We provide personal small CNC machines, CNC tooling, and many more CNC items

bob