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Y-axis lock upgrade of PM45M

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Dan Coleman

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#1
Thanks to mrpragmaticjim on You Tube for the tutorial for making the lever and linkage to upgrade the Y-axis on a PM mill. His inspiration came from cuppajoe from this forum. I had to make a few modifications to fit my PM-45M and use the available metric materials available. 20181016_122233.jpg 20181016_113616.jpg 20181016_120402.jpg

Dan Coleman
 

T Bredehoft

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#2
One more tweak for my PM25, which looks almost exactly like that.
 

hotrats

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#3
Nice. I remember seeing the mod on here, but had forgot about it. Your version looks great!
 

Dan Coleman

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#4
I actually mocked it up with 1/4 plywood to get the dimensions correct. The front and rear levers are opposites because you need more clearance on the edges facing center. It was difficult to get the measurement for the link. I turned points on the heads of two M8 bolts, inserted them in place of the current locks, layed a strip of plywood against them, and tapped with a hammer. Locate the set screw holes for easy access when everything is in the locked position.

Dan Coleman
 

hotrats

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#5
I actually mocked it up with 1/4 plywood to get the dimensions correct. The front and rear levers are opposites because you need more clearance on the edges facing center. It was difficult to get the measurement for the link. I turned points on the heads of two M8 bolts, inserted them in place of the current locks, layed a strip of plywood against them, and tapped with a hammer. Locate the set screw holes for easy access when everything is in the locked position.

Dan Coleman
Dan,
Thanks for the tips!
Just started Lee's video. See that it is 4 segments, so will take a while. Still got to get out and finish setting up my lathe.....
 

Dan Coleman

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#6
Sorry for the name mix up. It is MrPragmaticLee.
 

38Bill

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#7
Love this idea. Winter project for my 932 for sure.
 

petertha

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#8
I like the concept but I'll also offer another opinion favoring '2 singles'. On my somewhat similar RF45 style mill before I made a change to those clamping bolts which I mention below, I would always do the hunt around routine. Set the table to 1.000" lock the table using the stock screws. The DRO would indicate anywhere from 0.990 to 1.010. Loosen, re-set, jiggle tighten... rinse & repeat. PITA. It finally dawned on me to do this a different way. Approach the target, say 0.980" in this example, then just snug up one screw, creep up to 1.000" under some friction, then tighten the other to hold & snug hem both up. With this technique I stood a much better chance of it preserving the target position. More like +/- 0.001".Call it 'friction based anti-backlash'. LOL You might still be able to do this with both tied together, who knows.

But backing up a step. The problem I had with the stock screws was same as my lathe. When the screw goes up against the dovetail gib, yes it imparts clamping force. But it also screws against the upper portion of strip, applies a smidge of torque and displaces the table within the available back lash, kind of like a crude screwdriver. And that is the drift you see with an independent DRO. So what I made was a small contact shoe from round brass stock ~ ID of thread hole and ~0.3" long. On one end was an angle that matches the dovetail. On the other was a center drill or ball cavity if you have a ball EM. The bolt end was modified with a bearing ball attached with Loctite that engaged the shoe socket. Now when you tighten, the nice shiny ball applies nil torque, its linear displacement without the unwanted torque. And now the shoe presses & mates the dovetail at pure face to face contact. I can draw a picture but hopefully you get the general idea. This greatly improved carriage or table 'staying put'
 

pontiac428

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#9
Looks like a great idea! How do you constrain movement of the lever assembly to prevent the gib screws from bending downward when you engage the lock? This is a much needed modification.
 
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