Another obligatory New PM-833TV and PM-1340GT Ordered!

Janderso

Jeff Anderson
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Pardon me, but that's a waste of good beer!
You used the phrase "good beer" referencing IPA.
Sorry, I couldn't resist.
I prefer the golden fruits of Adolph Coors.
I know, my opinion is worth nothing :)
 

Christianstark

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Further information has uncovered that I have a significant taper at the thin end of my gib.

First showing me applying pressure to the fat end.
tempImageqoqEk1.jpg


Next shows me applying pressure to the thin end of the gib.
tempImageG48FAI.jpg


This is causing the gib adjusting screw to have issues getting a purchase on the thin end of the gib.

I have contacted PM for assistance.
 

davidpbest

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This is causing the gib adjusting screw to have issues getting a purchase on the thin end of the gib.

I have contacted PM for assistance.
I found the same, but decided to make my own scraped gib with precise fit.
 

B2

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Hi David,

I have gib problems with my PM940M-CNC and may have to make all of mine over. The Z-axis gib is too small and too short. In the mill case these gibs are trapezoids and taper in both width and thickness. Its thickness along the ~12.5" length varies from about 0.4" to about 0.3" but I figure is about .005+- too thin. I measured it pretty well and the thickness taper/slope is right at 0.0087 +- inch/inch slope. The width is currently incorrect, especially at the small end, and the locking screw head does not reach the gib at all, but slides up along side of it to pinch the gib into the way binding. So effectively not acting like a gib at all, but as a saddle lock. I have worked around this for now, but it has to go. Nevertheless, its width is about 1" and varies about 0.1 over the length. The diagonal of the trapezoid varies even more as it is larger. I have thought of more than one approach to making this trapezoid on thin material, but maybe you have a better way. Clamping is always a concern.

Can you point me to a description of how you might have proceeded to make yours? Thanks.

Dave L.
 

davidpbest

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Can you point me to a description of how you might have proceeded to make yours? Thanks.
I neglected to take photos and document the process which is a shame - I was frustrated and in a hurry. However, I basically followed the same process Keith Rucker describes in the video link posted below. His series goes on for 3-4 episodes, so watch the follow-up videos too. I did use cast iron, and finding a scrap of Durabar for this was probably the most challenging aspect of the project. I don’t have a surface grinder, so after machining the replacement gib, I did a lot of “hand honing” work on a surface plate with successive grits of sticky-backed sandpaper stuck down to the surface plate, hand rubbing the gib against the abrasive, and then grossly flaked it for oil retention. It’s not to NASA standards, but a heck of a lot better than want came with the machine. Hope this helps.

 

Christianstark

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The way edge does not look straight? Is this a photo deception?
The way dovetail is indeed sloped, but that is to accommodate a wedge shaped gib.The wedge + gib makes a straight slot to ride on the ways of the compound base. The gib it tightened by adjusting 2 screws at each end of the gib. loosen the thin side and tighten the thick side to tighten, and vise versa to loosen.
 

B2

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The way dovetail is indeed sloped, but that is to accommodate a wedge shaped gib.The wedge + gib makes a straight slot to ride on the ways of the compound base. The gib it tightened by adjusting 2 screws at each end of the gib. loosen the thin side and tighten the thick side to tighten, and vise versa to loosen.
I did not mean sloped. I meant straight. It looked bowed?.... so that a properly made gib would only be hitting a one points and so rocking.
 

Christianstark

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I did not mean sloped. I meant straight. It looked bowed?.... so that a properly made gib would only be hitting a one points and so rocking.
I see what you mean. I think it MAY be a combination of the taper in the gib, and maybe a roll off on the way. Here is another pic that shows the gib referenced to a flat surface.

tempImageXJ4M6R.jpg
 

Christianstark

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I did wind up cutting about 3/16" off the thin side of the gib, and it is now seating against the front gib adjust screw much better. I think the material removal reduced the taper a good bit, and the fitment is much better than it was.

I may wind up asking for a blank, and shooting for a better fitment, as the gib supplied still has probably 2mm of travel up and down within the dovetail, but as I have it set currently I am good enough for beginning to learn to thread.

@davidpbest that video you sent is fantastic!
 
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