G0678 CNC Conversion Build Log

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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Tue Feb 13, 2018 10:51 am

Progress Report:

Here is a picture of the front Y axis belt/pulley cover. This should keep the shirt tails out of the pulleys! :D

Spindle encoder is on the way as are the pulleys and the belts for the Z axis and the encoder.

Stay tuned, we'll be right back with a rigid tapping video after this commercial break! Yeah, right. There is still lots to do before I make any holes to tap.

Dave C.
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I learn something new every day! Problem is I forget two.

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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Sun Feb 18, 2018 1:51 pm

Progress Report:

I have the encoder mount almost complete, I just need to put the slots in for the mounting bolts and the three set screws to allow for alignment of the belt. I'm still waiting on the pulleys and belts for the X axis and the encoder.

The encoder mount uses two 10 mm bearings, a shaft made from W1 drill rod with a 10 mm x.300" step on the bottom end, a 8 mm x .400" step on the top and then a 10 mm step below that for the upper bearing. That leaves 1.440" in the middle to mount my 2.670" timing pulley of which there will be an exact match mounted below the 5" spindle pulley.

0218181223 (2).jpg

I also finished the tool change idea that lets me raise and lower the knee as needed to compensate for longer or shorter tools. The way this works is I set my part Z zero with my first tool. After I use that tool and I'm ready for a tool change I make a G28 call and move to my tool change position away from the part. With this .250" dial indicator and the mount I made from scrap, I can establish the height of the tool I set my Z, make a tool change and then just raise or lower the knee till the needle is at zero and I'm back to the same cutting height as I was before but with a different tool length.
0218181223a (2).jpg
So no tool lengths to set in my tool tables, just the tool diameters! I won't have to worry about getting tools back in the spindle at an exact height because I will make a quick measurement on every tool change. It is not as fast as having it all in the tool table but with a little less than 4" of Z travel I needed to come up with a way to compensate for a drill chuck, reamer and other tools that would exceed the 4" travel available.

We'll see how well it works once I get this all done.

Dave C.
Grizzly G0678 CNC conversion with Acorn in progress!
I learn something new every day! Problem is I forget two.

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GlennW
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Re: G0678 CNC Conversion Build Log

Post by GlennW » Sun Feb 25, 2018 7:29 pm

Not being able to lock the knee would have a significant affect on regidity and finish.

This is why bed mils are superior to knee mills even with the knee locked.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Sun Feb 25, 2018 7:52 pm

Not being able to lock the knee would have a significant affect on regidity and finish.

This is why bed mils are superior to knee mills even with the knee locked.
I agree that bed mills are far superior, but why say "not being able to lock the knee" because I can lock the knee at any height I wish?

Dave C.
I learn something new every day! Problem is I forget two.

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GlennW
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Re: G0678 CNC Conversion Build Log

Post by GlennW » Sun Feb 25, 2018 7:54 pm

If you are using it instead of the quill for the Z axis, would you plan on pausing the program every time you needed to make a Z move to lock or unlock it?
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Sun Feb 25, 2018 8:24 pm

Oh no, you've misunderstood how this is going to work.

The Z axis is the quill/spindle but it is limited to 4" of travel. However, 4" will do about anything I need to do except to make tool changes for long tools such at when I need to drill or use a reamer.

So I only move the knee to change the tool offset.

So basically it works like this. I lower the spindle to -1.000" and set that as my Z zero which will give me 1" of clearance to move off of the part. I insert my 1st tool, and raise the knee till the tool touches the top of the stock. (Locking the knee)

I start the program and run it until it calls for a tool change having moved to the G28 tool change position. I then set my tool change dial to that height and zero the face dial. Now I can insert the next tool manually and adjust the knee using my dial, lock the knee and continue on with the program.

All of my tools will have to be set with no length offset in my tool table in order for this to work but it is pretty much my only choice with this setup since I don't have a repeatable tool change system. (R8 spindle)

This machine is not intended for production work! It is just something for me to play with and make a part once in a while. Or throw it away and build something better but at my age, I think this is my last build.

It's not for everyone for sure but it is way better than the mill I'm using now.

Dave C.
I learn something new every day! Problem is I forget two.

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GlennW
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Re: G0678 CNC Conversion Build Log

Post by GlennW » Sun Feb 25, 2018 10:33 pm

Yes, I did misunderstand.

I thought you were not going to use the quill due to the backlash, and use the knee instead.

It turns out that I missed a page and thought that your post at the end of page 2 was the last post...
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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Re: G0678 CNC Conversion Build Log

Post by Harold_V » Mon Feb 26, 2018 2:55 am

Dave_C wrote:
Sun Feb 25, 2018 8:24 pm
All of my tools will have to be set with no length offset in my tool table in order for this to work but it is pretty much my only choice with this setup since I don't have a repeatable tool change system. (R8 spindle)
Dave,
Bridgeport used to market a quick change, which would solve the riddle of not being able to change tooling without losing the offset for the Z axis. It uses a Jacobs type chuck key to lock a #30 taper tool holder in the adapter. There was a reasonable number of bore sizes available, up to 1" if memory serves. Don't know if it's still on the market, though.

I bought one years ago when I had to make multiple tool changes in rapid succession on a production job. I don't use it often, but it's quite nice when needed. Surprisingly, while it extends from the spindle a couple inches, it appears to have reasonable rigidity. I'd recommend one if you find need in the future, if that's any help.

Very nice project, by the way. I've enjoyed following your progress and have been very impressed with your workmanship.

H
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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Mon Feb 26, 2018 9:11 am

I thought you were not going to use the quill due to the backlash, and use the knee instead.
Glenn, if the backlash issue becomes a problem I'll go back to my original plan and move the quill with a ball screw. I could not get the small size I needed from the same vendor I was using so I opted for this temporary solution. The backlash is about .020" but the weight of the quill and spindle will keep the tool down except when I drill so we'll just have to see if that works or not. I've got this all drawn up and it will make a good project for next winter!

Harold, I could not find anything from Bridgeport but I did find a very neat system from Royal Tools call the "Royal 8". It would solve the tool change issue but since I'm limited to 4" of Z travel I'd still be out of range when I go from end mills to drill bits. (it is a bit spendy and that is being polite)

It will be nice to see if this setup will actually do rigid taping as Centroid advertises!

Dave C.
I learn something new every day! Problem is I forget two.

BClemens
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Re: G0678 CNC Conversion Build Log

Post by BClemens » Sat Mar 10, 2018 9:21 am

This is how I did the quill on knee mill basically the same as is being converted here. There are magneto bearings back to back at the bottom of the ball screw and the minute 'lash' in the ball nut has never caused a problem. I started to use the rack gear on the quill for this but there was no way to reduce that backlash enough so that portion was clock spring preloaded to neutralize the weight of the quill/spindle assembly. The bearing housing for the original quill gear through the headstock was made eccentric to take up the gear backlash but this still didn't work out. The worm drive was done away with because actuating Z axis would have been far too slow. This has a DC servo motor with a USDigital encoder.
BC
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Dave_C
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Re: G0678 CNC Conversion Build Log

Post by Dave_C » Sat Mar 10, 2018 9:26 am

Yeah, that is closer to what I intended to do in the beginning. If i can find the right parts, I will still make the change next winter but for now it is going to be what it is.

Dave C.
I learn something new every day! Problem is I forget two.

BClemens
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Re: G0678 CNC Conversion Build Log

Post by BClemens » Sat Mar 10, 2018 9:33 am

Your project will be very appreciated in the future. I spent many, many hours on this one and never regretted a minute of it. Your endeavor to share this is commendable - never occurred to me even though photography is another hobby - but, seems I never have a camera around when I need one.

Keep on trucking!
Bill

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