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Powermatic toolrest holder seizing

Joe Cornell

Joe Cornell

Joined
Jan 3, 2006
Messages
61
Likes
420
Location
Kenmore, WA
The tool rest holder on my Powermatic 3520c seizes when I use any non-powermatic toolrest. I measured the only powermatic toolrest I have and the post is 0.995 inches diameter. Every other toolrest post I have is 1.0 inches diameter. The toolrest holder on the 3520b is designed differently and has no problem with 1.0 inch posts. Has anybody else noticed this? Any ideas on how to fix either the toolrest holder or my toolrest posts?
 
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Hi Joe. I don't own either of those lathes, so I'm doing guesswork here. 1" is an industry standard size, or at least in the USA. My first thought is that the toolrest hole in the banjo (i.e. the toolrest holder) is undersized those few thousandths you need for proper fit, especially since this is not an issue on the PM-B lathe. 0.995" makes sense for the post of the PM rest you have and that it fits, where the non-PM won't in the slightly undersized PM banjo hole. And maybe the "undersized" is only in one small area of the banjo hole, just enough to cause the problem.

Two choices. #1, you'll need to decrease the diameter of the steel posts of your non-PM rests. A "shoe shine" action with course sandpaper (probably silicon carbide vs. aluminum oxide) will eventually get you there. Or, #2, increase the hole diameter in the softer cast iron banjo a few thousandths, and this can be done with a "ball hone" chucked in a drill. Machinests and mechanics use them for cleaning out and final sizing any number of types of machine cylinders. Cheap to buy, and you have to be VERY careful not to over-do it it while honing the softer cast iron. Sneak up on the proper fit- keep a slower speed on the drill, run one or two strokes, wipe out the hole, and test fit. Repeat as needed until your other rests fit. WD-40 can be the honing lube for the process. Heck, skip the drill and stroke it by hand by fitting the hone into a turned wood handle, then hone the hole manually. 1" ball hone from Amazon (your local auto parts stores may stock them, especially NAPA stores)- https://www.amazon.com/Cylinder-Diameter-Diameters-Stainless-Materials/dp/B0GHMWD8ZV

Toolrest posts are not precision machined devices. That post is probably nothing more than simple cold-rolled steel rod (maybe hot rolled if they went cheap on their build), made in that 1" means 1" or slightly bigger, to then be machined down to a finished 1" or whatever the task requires. Will this hole honing make for a sloppy fit for your PM rest? Maybe. Should you combine honing out the banjo hole and shoe-shine sanding the toolrest posts to make them fit? Not a bad idea. Should you skip the honing of the banjo hole altogether and just sand the posts? That would work too, but it will take some work and time on your part. But, you need some way to make them fit. Just be "slow and go" about it so you don't create new problems. And good luck! Let us know how things work out.
 
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Steve Tiedman said:
Hi Joe. I don't own either of those lathes, so I'm doing guesswork here. 1" is an industry standard size, or at least in the USA. My first thought is that the toolrest hole in the banjo (i.e. the toolrest holder) is undersized those few thousandths you need for proper fit, especially since this is not an issue on the PM-B lathe. 0.995" makes sense for the post of the PM rest you have and that it fits, where the non-PM won't in the slightly undersized PM banjo hole. And maybe the "undersized" is only in one small area of the banjo hole, just enough to cause the problem.

Two choices. #1, you'll need to decrease the diameter of the steel posts of your non-PM rests. A "shoe shine" action with course sandpaper (probably silicon carbide vs. aluminum oxide) will eventually get you there. Or, #2, increase the hole diameter in the softer cast iron banjo a few thousandths, and this can be done with a "ball hone" chucked in a drill. Machinests and mechanics use them for cleaning out and final sizing any number of types of machine cylinders. Cheap to buy, and you have to be VERY careful not to over-do it it while honing the softer cast iron. Sneak up on the proper fit- keep a slower speed on the drill, run one or two strokes, wipe out the hole, and test fit. Repeat as needed until your other rests fit. WD-40 can be the honing lube for the process. Heck, skip the drill and stroke it by hand by fitting the hone into a turned wood handle, then hone the hole manually. 1" ball hone from Amazon (your local auto parts stores may stock them, especially NAPA stores)- https://www.amazon.com/Cylinder-Diameter-Diameters-Stainless-Materials/dp/B0GHMWD8ZV

Toolrest posts are not precision machined devices. That post is probably nothing more than simple cold-rolled steel rod (maybe hot rolled if they went cheap on their build), made in that 1" means 1" or slightly bigger, to then be machined down to a finished 1" or whatever the task requires. Will this hole honing make for a sloppy fit for your PM rest? Maybe. Should you combine honing out the banjo hole and shoe-shine sanding the toolrest posts to make them fit? Not a bad idea. Should you skip the honing of the banjo hole altogether and just sand the posts? That would work too, but it will take some work and time on your part. But, you need some way to make them fit. Just be "slow and go" about it so you don't create new problems. And good luck! Let us know how things work out.
Click to expand...
Thank you Steve. I
 
I’ve had the same issue on my 3520 C, Joe. I posted it here some time ago. I notice it when I use a Robust rest. Curiously, it is not an issue with my Robo Hippy Rest. I have to give the Robust rest a bit of a smack to free it from the banjo. Not a killer issue, but just a bit of a bother. I’ve tried a bit of emery paper and also keeping it waxed or otherwise lubed. Helps for a while but goes back to sticking. I suppose I should give it more attention with the emery paper.

https://www.aawforum.org/community/....23730/#:~:text=While on the,nudge to loosen?
 
Well, after our club demo last week, I remember Dale Larson commenting that the single set screw for tool rest securing is just about worthless. Robust lathes have the double wedges that pinch the tool post into position, and it is far more secure than the single set screw. With the set screw, you just don't get tie secure grip. I did have a 3520A, and I ended up having a second set screw made since there were 2 holes on the banjo post hole. I got rid of the cheap pot metal handle and used a sliding T handle like is found on most vices. That worked far better. I think, when the 3520C came out they did have the wedges, but I don't think they make those that wan any more. I would think they would want a D shape or some thing like that so they don't rotate/spin like mine do.

As for tool rests fitting into the post hole, for me, it is more about the inside rusting since I love sloppy wet wood. Even if water does not get down inside the post hole, I will occasionally lube the post with some slick stick or Glide Cote. Some times even some 3 in 1 oil. The other option is to sand the post down slightly.

robo hippy
 
The 3520C model has the pinch wedges as well. I have 3 Robust rests and none of them seize. I have 2 others that are an off brand and they seem to work well. I'm hardly an expert, but I think I'd take those wedges out and clean everything in the banjo and see if that solves the problem.
 
I have a 3520C. I have both PM rests and Robust rests. I found that both rests started sticking. I found the problem was caused by the wedge mechanism that holds the tool rest post in the banjo. There is a spring that is supposed to push the 2 wedges apart. I found that the spring would become misaligned and was not push the 2 wedges apart causing the tool rest to get stuck.. I reworked the spring so it fit properly and it hasn't seized since.
 
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