Remove Lathe Compound for CNC?

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SteveHGraham
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Remove Lathe Compound for CNC?

Postby SteveHGraham » Sun Jul 03, 2016 12:02 pm

Because the CNC mini-lathe is up and running, I am now thinking beyond the basic puzzles such as how to turn it on.

I was running it yesterday, cutting a bench dog out of a mop handle type of thing, and I kept having problems with the cross slide.

A mini-lathe is supposed to have a 7" swing, so theoretically, you can turn 7" parts on it. The my converted lathe fails to live up to expectations. The compound is set up so the tool post is WAY out on the far end. If you try to pull the tool tip back to where you can cut a big diameter, the cross slide runs out of room. This is particularly bad for CNC, because it's easy to tell the lathe to ram the cross slide up against the motor mount. The lathe now works best when the compound is turned around with the tool post near the operator, but because the dial is in the way, I can't turn it 180 degrees.

On top of all this, a mini-lathe compound is wobbly. It lacks rigidity. The farther you back it out, the wobblier it gets.

It seems to me, in my vast CNC knowledge, that the compound is unnecessary for CNC. It has to stay in one position in order for the tool to be where the computer thinks it is, so an adjustable compound is not helpful. I'm thinking I should remove the compound, put it in a bag, and replace the whole thing with a block that sits on the cross slide.

Thoughts?

I am attaching a photo of the lathe in action. You can see the dial is on the far side.

07 03 16 CNC mini lathe cutting wooden bench dog.jpg
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SteveHGraham
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Re: Remove Lathe Compound for CNC?

Postby SteveHGraham » Sun Jul 03, 2016 3:55 pm

For now I will answer my own question.

I looked around and found that other people had the same idea. Today I made an aluminum block that will attach to the cross slide, and this week I plan to drill it and stick the tool post on it.

These little lathes are funny; the advertise them as "7x," but when you get the tool mounted, that seven looks a lot more like a 2.
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Harold_V
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Re: Remove Lathe Compound for CNC?

Postby Harold_V » Sun Jul 03, 2016 4:01 pm

The swing of a lathe is determined by the diameter that can be mounted and turned over the ways/carriage wings. The swing over the cross slide will always be less, so the idea that your 7" lathe can turn only about 2" is in keeping with what you should expect.

My Sag 12 Graziano is a 12" machine, but can't turn anything larger than about six inches, aside from the area near the chuck. Because it has a natural gap (the tailstock ways terminate short of the chuck, and the carriage ways are well below the tailstock ways), I can turn an object 17-3/8" in diameter.

Harold
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SteveHGraham
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Re: Remove Lathe Compound for CNC?

Postby SteveHGraham » Sun Jul 03, 2016 4:32 pm

Seems like mini-lathes are particularly bad. The one I'm modifying is fixed up so you can put the cutter way out past the lathe's axis, but there is very little room in the other direction, where travel could be more useful.
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Dave_C
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Re: Remove Lathe Compound for CNC?

Postby Dave_C » Sun Jul 03, 2016 7:39 pm

Steve,

If you can find the thread where I did the CNC conversion on my Grizzly G4003G [12X36] you can see what I did. I had about 6" of X travel when it was a manual machine but after the conversion I now have 7.5" of X (cross slide) travel.

The compound is gone for the reasons you stated. It was not a very ridged setup! The solid block for the tool post works very well and I never need to change the tool post once squared to the chuck.

I recommend removing the compound for a CNC machine.

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

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SteveHGraham
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Re: Remove Lathe Compound for CNC?

Postby SteveHGraham » Sun Jul 03, 2016 7:52 pm

Thanks, Dave. I didn't see that thread before I got to work today, but I did improve the lathe. Here is a photo.

The lower part of the block doesn't really do anything, and it may get in the way. I left it there in case I thought of some reason for adding an attachment or something.

07 03 16 CNC mini lathe with new cross slide mount.jpg
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hanermo
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Re: Remove Lathe Compound for CNC?

Postby hanermo » Thu Jul 07, 2016 8:49 am

I removed my compound on the 7x.
I also removed my compound on the heavy 12x industrial, and a very high end CNC refit.

The toolpost mount is now a 180x240x50 mm steel block.

Next move onto Mach4.
Next, working on finishing the MPG, and then a Y axis.
Maybe a more rigid C axis via planetary gears.
New servo for tailstock (B axis).
Auto clamp for chuck or collet chuck.
Fit the toolchangers (2 of).
etc..


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