Grizzly G9729 Horizontal Lead Screw

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johnnybar
Posts: 4
Joined: Tue Nov 22, 2016 4:59 am

Re: Grizzly G9729 Horizontal Lead Screw

Post by johnnybar » Sat Nov 10, 2018 7:06 pm

You can try tinning the old nut with lead free solder and seating it into the leadscrew with heat. If your leadscrew isn't hourglassed, it will give you near zero backlash and can be redone as needed indefinitely for almost no cost.

johnnybar
Posts: 4
Joined: Tue Nov 22, 2016 4:59 am

Re: Grizzly G9729 Horizontal Lead Screw

Post by johnnybar » Sat Nov 10, 2018 7:08 pm

Here's another poster's (KB3AHE) process from another forum:

1. Dissassemble and remove the crosfeed screw and nut, clean all of the oil and mung out of the crossfeed nut threads. (I used a gun brush to get them shiny clean)
2. Heat and flux the crossfeed nut threads with standard "soldering paste" flux. After several applications of heat and flux, solder up the threads of the nut with
the new lead-free plumbing solder. (The new tin-silver stuff is a lot harder than the older lead-based stuff.) and let cool.
3. Heat the nut up again and tap it on the bench to knock out all of the excess solder. (You basically just want it to be "tinned" all of the way around)
and let it cool off again.
4. You will now find that the crossfeed screw won't go into the threads, or at least not easily. (If it does, add some more solder)
5. Leaving the oil on the crossfeed screw, gently reheat the nut until the screw goes through the nut and allow it to cool. (If it gets too tight after it cools, heat it and work it a little more.)
6. Clean all of the oil and grease off of the screw and out of the nut and reassemble it into the carriage dry. Use the power crossfeed to run it back and forth a couple of times. (This will wear it in.)
7. Oil the screw and nut up real well and run it back and forth a few times, and you will be very happy with the reduced backlash you now have.
8. Also be sure to check and adjust the end play in the screw at the dial, and also check for slop where the crossfeed nut is attached to the cross slide.

pete
Posts: 1503
Joined: Tue Feb 10, 2009 6:04 am

Re: Grizzly G9729 Horizontal Lead Screw

Post by pete » Wed Nov 21, 2018 2:23 pm

Since you mentioned frequent cleaning and oiling that shouldn't be the issue. However if it's wearing like you say then somethings obviously not correct. Possibly the factory is using soft brass for the half nut threads instead of bronze. Roughly finished flanks on the leadscrew could be another possibility. I've also read more than a few times about non standard ACME screws being used so I'd want to very accurately measure and not just take Grizzly's word on it to be 100% sure of exactly what you have. Decent quality or far better than that ACME screws and nuts aren't hard to find. The tighter the accuracy specifications for allowable pitch deviations the higher the price goes (naturally) But if I was having issues like you are I'd seriously consider replacing both the leadscrew and half nuts with something a lot more durable. The half nut actuating assembly is usually pretty sloppy and poor fitting on this equipment so a bit of re-machining and building a few new parts in that area might be expected. Then soldering the new bronze nut in place and splitting it. Yeah it would be a fair amount of work, and you can expect to also machine both ends of the leadscrew ACME rod to fit your machine. Since the OEM parts aren't lasting like they should then fixing the problem properly seems like the most logical solution to me. If you decide to go that route then buying at the lowest possible price might get you the same issues you already have. Nook Industry's and Thomson are 2 of many that make high quality ACME screws and matching nuts.

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tornitore45
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Joined: Tue Apr 18, 2006 12:24 am
Location: USA Texas, Austin

Re: Grizzly G9729 Horizontal Lead Screw

Post by tornitore45 » Wed Nov 21, 2018 5:32 pm

The replacement half nut was some white metal instead of brassy bronze, I was afraid it would wear out even faster. I found that there was room to extend the half nut length. Not the entire Nut, but a sufficiently beefy cylindrical extension on both sides. I bored out the worn threads and silver brazed a longer insert threaded single point.
My lathe is a 9x20 so we are talking about a much smaller nut.
Mauro Gaetano
in Austin TX

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