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Machine PDM30 table nut stripped
- Thread starter Brian H
- Start date
Machine
This is a problem we all face from time to time. If you don't have the required tools or the required skills you need to find a friend who does or find them used, or find a different way, or buy more tools.
Where are you?
Danzo187
Member
had the same problem with my grizzly mill ,that capscrew is for taking backlash out,the jam is from chips and crap getting in there ,the nut is much softer then the screw ,you can work it out (wax on wax off) you might end up with some deformation on the nut but will be quite useable once cleaned
table nut threads are worn so cleaning wont improve
The thought I had is to bore out to 1-10 acme thread but indeed, I do not possess the skill nor components to ensure that it turns out correctly. This would reduce the nut wall thickness but maybe there could still be enough to make the nut usable again (?)...then take a 1-10 acme rod and turn ends down to match the OEM leadscrew.
The thought I had is to bore out to 1-10 acme thread but indeed, I do not possess the skill nor components to ensure that it turns out correctly. This would reduce the nut wall thickness but maybe there could still be enough to make the nut usable again (?)...then take a 1-10 acme rod and turn ends down to match the OEM leadscrew.
Danzo187
Member
if you have some brass you can put the crossfeed back together and turn a light press fit onto the boss and mill the top square then drill and tap 1/2-10 LH acme thread,
then if you need make the 5/8-8 RH hell why don't I send you the ones I took out of mine there still quite useable,send me your address and i'll put them in the mail...no charge
then if you need make the 5/8-8 RH hell why don't I send you the ones I took out of mine there still quite useable,send me your address and i'll put them in the mail...no charge
Danzo187
Member
he
res a pic of nuts very good threads
Attachments
I have a similar set of screws/nuts that i bought for a project that never happened. They are in pretty new condition and were removed for a cnc conversion when the mill was nearly new. Send me the lengths and i can see if they are the same.
Mine are 36" and 17.5" approximately, within 1/4" .
Mine are 36" and 17.5" approximately, within 1/4" .
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This is what my X axis nut and lead screw look like. There is a fair amount of backlash and this is not adjustable on my mill.
The nut is mounted in this hole.
Looking like this.
This is the plan for a 25mm ball screw.
Instead of mucking about with poor quality replacement ACME screws and nuts it might be, in the long run, better to go this way?
The nut is mounted in this hole.
Looking like this.
This is the plan for a 25mm ball screw.
Instead of mucking about with poor quality replacement ACME screws and nuts it might be, in the long run, better to go this way?
I've thought about doing that too John. But it isn't without problems of its own so I abandoned the idea.
There are lots of threads on line about how to improve a leade screw nut. Typically either putting a slit and jack screw in it or cutting it in half and installing guidepins and adjustment screws.
In the end, I decided my mill is good enough and I don't plan to do anything other than use it. My DRO eliminates reading errors and without them it's easy to compensate for the backlash.
If I ever change my mind, I'll prolly go with an all-new nut with guide pins as that's the best solution I've seen.
Is that with or without CNC?
If without, I'm interested to know how you handle the inertia and overshoot. Or at least how you feel about it.
This is what I came up with for the anti-backlash nut for mine. If I was going to make one. What I have found with mine and the 0.027" backlash is that with a larger end mill and climb cutting it will literally bite into the material and pull the table away from the driving surface of the lead screw.
But I figured if I was going to go that far then a ball screw carrier wasn't really that much more work. It's on the list. #42.
The problem with ball screws is that pressure on the nut can drive the screw. It's why, with power off a vertical screw can be spun and for example the mill knee will self drop to the lowest position. With hand milling I believe you have to be diligent about locking the axis you aren't turning by hand.
its an ex cnc, but i operate it manually. No inertia or overshoot. its not that free. It is possible to back drive them though, which on a facing cut is not a problem at all. On a hard side mill or slotting/shoulder type work, you do want to lock the unused axis, but that becomes routine pretty quick. Its very nice to be able to dial in a very precise location due to zero backlash. The preloaded nuts allow you to tap the handle to a tenth pretty easily.
I don't think this is unusual. Most of us have broken a few end mills that way.
It's not the work, it's the fly away table that worries me.
on a heavy side cut using the x axis to feed, the y, if left unlocked might move a few thou. It certainly doesn't fly away.
Yes. I could tighten the gibs way more. But that doesn't really solve the problem which, as the photo shows is an absolutely crap acme nut. And this isn't something you can look at before you buy the machine. Once the power draw bar project is done this or the knee ball screw was next on the list.