Hi I got an almost new palmgren compound table and one of the screws looks bent on the turned down end where the handle and bearing are. I haven't had much time to look at it yet but I'm hoping to bend it back as straight as I can and use it until I can either make a replacement or possibly fit a ball screw. I don't know if the metal is hardened yet but I doubt it is. Ill check with a file before I try bending it. Has anyone done this before any hints to get it good and straight? I'm a little worried it will just snap off when I try to bend it back so I was thinking about heating it with a torch but would prefer not to. I'm thinking I will just put the straight part in a padded vise and slip a pipe over the bent end and bend till straight. Is this the best way?
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Fixing a bent acme screw?
- Thread starter Ebel440
- Start date
My method of choice for "precision" straightening is a hydraulic press. I find the bet control over how far I am overbending to compensate for spring back. I have straightened a number of prop shafts, and use a dial indicator to repeat or move a little more if needed during the process.
Your idea of putting a sleeve (pipe) over the stub end is good, but you still should choose your bend points carefully. You might do just fine on a vise screw that way though. I think I would put a generous (full) radius on the sleeve (pipe) ID so as not to concentrate all the force at a "corner" and create a new stress point. The screw should not be too hard to bend. It bent once already, right? If it is indeed hard, a torch would soften it and make for safer bending, at the sacrifice of wear at that point. That may or may not be a real worry.
Your idea of putting a sleeve (pipe) over the stub end is good, but you still should choose your bend points carefully. You might do just fine on a vise screw that way though. I think I would put a generous (full) radius on the sleeve (pipe) ID so as not to concentrate all the force at a "corner" and create a new stress point. The screw should not be too hard to bend. It bent once already, right? If it is indeed hard, a torch would soften it and make for safer bending, at the sacrifice of wear at that point. That may or may not be a real worry.
Hi, I have restored several Palmgrens. The feed screws that I have worked on are not hard and were straightened very easily. But, the cast aluminum handles that got bent as well are a different story. To straighten the shafts take a long straight (longer the better) say 2’ X 1” dia round alum stock and machine a hole in the end for a SNUG fit on the journal of the shaft end. Put the shaft in a soft jawed vise, align and gently bent. Note: only bend/straighten where the original bend is, support the rest in the vise. Use the length of the alum stock as an indicator of straightness. You can roll/turn everything and very easily see any error. You can even chuck the screw in your lathe and watch the alum stock rotate for trueness…Good Luck, Dave.
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Use a press if you have it with an indicator if possible. Put it between vee blocks on a surface plate to identify where it needs it and by how much. If you don't have a press a vise with soft jaws sounds good as was mentioned before.
Just make sure you really take your time. Lots of patience is important.
Sent from my SAMSUNG-SGH-I317 using Tapatalk 2
Just make sure you really take your time. Lots of patience is important.
Sent from my SAMSUNG-SGH-I317 using Tapatalk 2
I got the screw out and made an attempt at straightening it using aluminum blocks in my bench vise as a press but my little bench vise didn't have enough strength to bend the 10 mm shaft enough. I did straighten it some but need to bring it to my work and use a real press. My plan to fit a pipe over the end and bent won't work as the bend is in a curve over a 3 inch length. It also looks like the turned down area may not be concentric to the screw. I'll check it out at my work where I have the proper tools to do the job. I'm not very satisfied with the quality of construction overall I bought a palmgren over a cheaper company hoping it would be well built. The casting do seem well made and put together but neither of the screws are great. But I bought it knowing it was damaged so no returning it. I do have a brand new ball screw I got from the Bridgeport factory when they auctioned everything off but it may be too short I'll have to dig it out and see if it'll work. I bought the table to convert to cnc to experiment with so I'll most likely have to modify some things anyway.
If you don't have a press, you can try doing what I've done several times. The challenge was to straighten the bar of a linear bearing set (bent by a co-worker's accident, not by me!)
I placed the bar (bearing blocks removed) across a couple of hardwood blocks on a Bridgeport mill table, held a piece of plywood under the (fully retracted and locked, no tools mounted) spindle, and used the knee to slowly bring the table up and un-bend the bar. As mentioned by others, there will be some spring-back. The nice thing about using the knee is that you can go again, and the dial or DRO lets you know where you were/are. So you can "tweak" it a few thous at a time.
This trick should DEFINITELY NOT be used for large parts, as it would probably damage the knee. But for something the size of a vise lead screw, it should be OK.
PS - has anybody tried adding a DRO to a hydraulic press? I'd bet it could come in handy for fine tuning bends, etc.
I placed the bar (bearing blocks removed) across a couple of hardwood blocks on a Bridgeport mill table, held a piece of plywood under the (fully retracted and locked, no tools mounted) spindle, and used the knee to slowly bring the table up and un-bend the bar. As mentioned by others, there will be some spring-back. The nice thing about using the knee is that you can go again, and the dial or DRO lets you know where you were/are. So you can "tweak" it a few thous at a time.
This trick should DEFINITELY NOT be used for large parts, as it would probably damage the knee. But for something the size of a vise lead screw, it should be OK.
PS - has anybody tried adding a DRO to a hydraulic press? I'd bet it could come in handy for fine tuning bends, etc.
So I brought the screw to my work and used the press. I managed to get it a lot better then it was but its still not perfect. I just can't seem to get a little bit of kink out of it. It's still showing about .02 variation when I spin the shaft in v blocks. I tried putting the table back together to see if it would work as it is and it does work but I'm not happy with it, it still drags a little bit. Since the threaded portion is perfectly straight I'm thinking ill cut off the entire end and drill and tap it. Screw a new piece of metal in and turn it to 10mm and be done with it.