A benchtop cnc lathe build

[S_J_H]

Thanks Ron!
A couple progress pics.
Steve

[rustamd]

its looking good!

[Builder4wd]

Hi,

You mentioned that you used Starrett ground stock. Where did you buy it? Whenever I see any ground stock, it's always extremely expensive.

Thanks!

[rustamd]

Hi,

You mentioned that you used Starrett ground stock. Where did you buy it? Whenever I see any ground stock, it's always extremely expensive.

Thanks!

i would want to think that Starrett would be twice expensive than normal no brand just becouse of the name

[S_J_H]

I used precision flat stock from Enco and Starret.
Using this material will save A LOT of machining time but do not think for a second you can build a precision machine with it without final surfacing of all critical surfaces.

I broke down my lathe today to just the bed. I took it over to my friends shop and he tossed it on one of his big Mazak vertical centers and cut it nice and flat on the bed surface and rail risers.

Made a big difference and I found out just how far off I really was.

I remounted the long rails and was able to quickly align them to a .0001" parallel variance in almost 18".
I still have a slight vertical bow of .0005" over 18". However that will be totally inconsequential in turning operations.
Steve

[zephyr9900]

...cut it nice and flat on the bed surface and rail risers.

What surface did you set up on to do that, Steve? You said earlier in the thread that the Z rail risers are bolted on. Did he face the bed surface without the risers and then the risers after they were bolted back on? And did he face the bottom of the structure also? Just being curious.

What a great lathe that is shaping up to be! And thanks for posting the bottom view of the bed over on deferr's thread.

Best regards,

Randy

[S_J_H]

Randy,
The rail risers were still bolted to the complete bed assembly. Those will NEVER be removed.
So first he surfaced the bottom side of the bed. Then flipped it over and surfaced the rail risers, head stock surface and down the middle of the bed where the tail stock locking post will move.

A little more adjusting last night and I can guide my test indicator the entire 18" and see no movement.

Steve

[Rube]

Damn Steve...you'll have to give me a tour of that beauty too when I stop over to check out he X3 conversion. You do some NICE work!!!!!

[Oldmanandhistoy]

Steve is your test indicator seized ?

Lol only joking ; very nice lathe you have coming on there do wanna sell it?

John

[S_J_H]

Rube, Thanks, you'll be able to check it out.
John, not for sale.

Oh man, I am sure getting a lesson in setting linear rail parallelism and how flexible steel is. I made a big mistake by thinking I could set the rails straight with just 1 linear block riding them and not having the headstock and motor assembly in place. I should have known better.

After bolting the head stock and motor down and reinstalling the carriage with all 4 blocks my parallelism for the long rails read a whopping .001" out.

So I loosened and reset them tonight. It's a long tedious process. Getting them to a total variance of .0005" is child's play. Getting them parallel to .0001"-.0002" is very time consuming. I do not have pusher blocks or a reference straight edge.
It's a time consuming process with a jackscrew and C-clamp. I mount a test indicator on the carriage and indicate off of the straight edge of 1 rail. Then double check by indicating the opposing rail. In the process I have identified 1 trouble area that fights me. It's to the far left edge of the rails right near the headstock. I noticed that just a slight preload force between the 2 rails in this area makes a nice difference in the parallelism along the entire distance. It eliminates much of the slight variance I see. A little Bed Twist? Must be.
So I made a neat little floating spring loaded friction damper with 1 rubber end placed between the rails right at the headstock. Works great to get that last tenth of parallelism. Might even absorb some vibration.
I'll snap a pic of it tomorrow.
In any case I have the carriage running real nice and straight now. I'm going to be checking this often to see if it moves.
I also plan on doing some tool tip deflection tests against my bigger 9x20.
Steve

[zephyr9900]

So I made a neat little floating spring loaded friction damper with 1 rubber end...

Steve, I think I have one of those holding the toilet paper roll on the wall brackets.

Seriously, though, I would be interested to know what your "twist" is without the spindle motor installed. Open sections like your bed have comparitively little torsional rigidity (vs. bending). And you said you faced the headstock spacer so it should not be inducing twist on its own. The off-center weight of the spindle motor might be doing the job.

I faced a similar situation with my Sherline mill. Its headstock (designed for maximum versatility) had the weight not only totally in front of the column, but also biased toward the side by the spindle motor. In optimizing mine for CNC, I made a bracket to put the motor behind the column, neatly balancing the headstock and putting the center of gravity right at the ways. In that case, it was not for column twist, but just because the off-center weight caused a lot of friction in the Z motion. I've thought of doing a similar thing with my Sherline lathe--relocating the spindle motor vertically over the headstock. The Sherline bed is similar to yours (open at the bottom) but is a thin-walled zinc or aluminum diecasting and reeeeealy flexible.

Best regards,

Randy

[pacosoide]

Hi ProtoTrains, that is a nice mod for you Sherline mill.
Do you have a website where you describe your procedure(s) to do this repositioning of the motor?
Thanks, Joe.