Machine PDM30 table nut stripped

[jcdammeyer]

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.

I don't think a ballscrew driven table turned by hand will fly away on the axis that is being turned. It's the non-active axis that could be pulled or the knee, that with gravity would slowly creep downwards with machining vibration.

 

[Darren]

I have ballscrews on x and y. Not on the knee. I'm just saying that for 99% of the work, its not an issue at all. When doing the finish pass lock the unused axis and its good.

FYI, my ballscrews are 5.08mm pitch or 0.200", not very fast screws. a 10mm pitch screw would certainly be a problem in a manual application

 

[Susquatch]

And this isn't something you can look at before you buy the machine.

I think you can get a feel for it. I used to bring a flashlight and long screwdriver with me.

If the leadscrew is worn in the middle, then it's a good bet that the nut is too. If the leadscrew isn't worn but there is a lot of backlash, then the nut needs work.

I'd rather fix a nut or make a new one than have to get a new leade screw.

But given @Darren and your comments, I won't be afraid of replacing both with a ball screw.

I wonder what a Bridgeport size set costs these days.

 

[Darren]

I found a new screw for my x axis on ebay. It is 32mm vs the original 25mm, so the yoke had to be modified for the larger ballnut. I also had to modify the end where the servo drives it to retain the original bearing arrangement and pulley in case i ever buy a cnc controller for it.

New guy from Murillo (Thunder Bay) Ont

Hi all, glad i found this site. I'm an automotive tech with a large shop slowly filling up with machine tools. So far I have a Standard Modern 1660 10hp lathe, Emco V13 13x40 lathe, Kent 1054hs bridgeport clone that was once a cnc mill. These were all college machines and in very nice...

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[PeterT]

FYI, my ballscrews are 5.08mm pitch or 0.200", not very fast screws. a 10mm pitch screw would certainly be a problem in a manual application

This is a key point IMO. From the reading I did on this a few years back, I get the impression that balls screw pitch has a lot to do with varying opinions ranging between 'runaway freight train if I even push on the table' to 'its fine'. Where I ran into issues was finding what I considered sufficiently fine enough pitch AND nominal imperial to match my dial AND the bearing housing wasn't sufficiently compact cross section to fit the often constrained table/casting cavity compared to conventional leadscrew & ABL nut. AND price of course. Also I've heard ballscrews don't lend themselves as well to other machining ops required to make them fit older machine configuration - diameter reduction, threading, cross pinning... although I have no direct experience there. It was collectively enough for me to pursue lesser of evils & just come up with a better ABL system on conventional leadscrew. The slit ABL works, but its not exactly elegant.

 

[Susquatch]

It was collectively enough for me to pursue lesser of evils & just come up with a better ABL system on conventional leadscrew. The slit ABL works, but its not exactly elegant.

Excellent summary of the issues and pretty much confirms my feelings about it too.

I've bookmarked this little discussion for the future.

I won't be as fearful of a ball screw next time, but I bet the end result will still be a new nut. Great discussion for anyone buying a used mill with a well worn screw too.

 

[ttlrfrank]

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" .

PM sent

 

[Darren]

@PeterT the ends of my ballscrews are not hardened and machine very nicely, both old and new. I mated them together on the end to keep the original configuration. I was able to find plenty of 5mm pitch, but not 5.08/0.200" to match what was there. I got lucky on ebay.

 

[PeterT]

Thanks for info, good to know

 

[Model Citizen]

For the record, I have a Grizzly G1007, build date 6/04 that also has a .925-10 X leadscrew.
I suspect mine & the PDM30 are almost identical machines.
my adjustable X leadscrew nut looks like Brian’s in post #6.
I adjusted the nut with a 4mm allan on a long extension
years ago to remove some backlash.
I was afraid to tighten it any more.
it still has about 30 thou backlash, but isn’t any worse than a few yrs ago, I keep it well oiled.
I have DRO on all axis, so easy to live with.
I called Grizzly yrs ago, they weren’t sure which nut I had.
the leadscrew does not seem to have any wear, just the bronze nut.
if anyone has a part # for the adjustable bronze X nut
please post it.

 

[Larry_C9]

I had a cross slide nut on a lathe do that years ago and got a new nut which wasn't much better. They were made so poorly that the nut would only engage about 1/2 the depth of the tread on the lead screw. I ended up making a tool bit that fit the lead screw and machining my own nut. There was room so I made the nut longer. The nuts I machined lasted a lot longer than the ones from the manufacturer.

 

[Model Citizen]

I just called Grizzly again, they gave me part# 1005423 for the X leadscrew nut. They call it a table nut.
It’s $106.95 usd, I just ordered it.
My guess it’s the same part for the PDM30.
That nut has 2 mounting ears on it, is adjustable & it’s bronze. And while I’m up for the challenge of making it, seems like re-inventing the wheel at this point, it’s lasted 19 years, & at that price I’ll just buy it.
I’ll report back when it arrives & I install it.
I hope this helps someone else.

 

[Susquatch]

I just called Grizzly again, they gave me part# 1005423 for the X leadscrew nut. They call it a table nut.

Grizzly has excellent service manuals written in good English and they maintain a very good supply of parts. I've always been very impressed even when my machine wasn't a Grizzly!

 

[jcdammeyer]

Grizzly has excellent service manuals written in good English and they maintain a very good supply of parts. I've always been very impressed even when my machine wasn't a Grizzly!

That's why I refer to my machine as a G3616 and the one with the horizontal mill feature as a G3617. The manual is way better than what came from House of Tools and they are identical machines except for the colour.

 

[Larry_C9]

I have found that the electrical system is sometimes different in a Grizzly than a Craftex even thought they appear to be the same machine.

 

[Susquatch]

I have found that the electrical system is sometimes different in a Grizzly than a Craftex even thought they appear to be the same machine.

This is where we usually get trapped into a debate about what "the same machine" means.

I think Grizzly orders similar machines from "the factory" as other resellers do but they often upgrade the parts, tolerances, electrical, accessories. Sometimes even specifying upgraded major components like spindles, bearings, etc. Whether that makes them different enough to be a different machine is a matter of opinion and debate.

I've been told that the owner of Grizzly and the owner of Busy Bee are brothers......

 

[whydontu]

There is sone overlap between Grizzly and Busy Bee. Depending on my degree of laziness and urgency, I buy from either. Especially now that BB has closed their office in BC. Used to be an hour to get to BB, or 1-1/2 hours to drive to Grizzly in USA (depending on how bad the border lineup is at any given moment). About 90% of my attempts to sub Grizzly parts into BB machines have been successfull, and Grizzly is a zillion times easier to deal with than BB.

BB in Vancouver was a cramped junky-looking store. Grizzly in Bellingham looks like a high-end car dealership and you could eat off their displays.

And yes, the owners are brothers and had an agreement not to poach into each others territories, but Grizzly started shipping to Canada a few years ago so maybe the agreement has changed.

 

[Model Citizen]

My X leadscrew nut arrived yesterday from Grizzly.
I did some measurements, & it is indeed for my .925-10 leadscrew.
It was $106.95, $115.29 USD total delivered to the house with free shipping.
I’m too busy to install it now, it’ll be this winter. I’ll report back then.
hopefully it’ll alleviate the .030 backlash (with all the adjustment taken up).
part # is on the bag In the pic. Grizzly calls it a table nut set.

 

[Tom O]

Glad to hear it fits. I would have thought the gap for taking out the endplay would have gone at least 1/2 way.