Grizzly G9729 Horizontal Lead Screw

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LX Kid
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Grizzly G9729 Horizontal Lead Screw

Post by LX Kid » Thu Jan 28, 2016 5:34 am

I have the Grizzly G9729 17x31 and would like to try my hand at making my own half nut. At $75 a pop I need a spare or two. I've already replaced it once and they wear fast even when frequent cleaning and lubing. Question "is" does anyone know what the Acme type/TPI/pitch is for the lead screw. A tap is around $100 and want to order the correct tap. American Standard/ Metric etc. Thanks

Harold_V
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Re: Grizzly G9729 Horizontal Lead Screw

Post by Harold_V » Thu Jan 28, 2016 4:22 pm

Such threads are generally created to standards, so a simple measurement of the existing screw should indicate what the correct tap should be. Once measured, you can check Machinery's Handbook to find identical readings. Measure the OD of the thread, using a micrometer. If you discover a reading in keeping with Imperial measurement (example, the screw measures .625" diameter), then count the number of threads in an inch.

Same thing for Metric, although in that case you must know the length of a full thread (in mm's). Diameters and lengths should be in multiples of .03937", if you don't have metric measuring capabilities.

Harold
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Carm
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Re: Grizzly G9729 Horizontal Lead Screw

Post by Carm » Thu Jan 28, 2016 4:33 pm

Type making acetal leadscrew nuts into your search engine and see what you think

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WesHowe
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Re: Grizzly G9729 Horizontal Lead Screw

Post by WesHowe » Thu Jan 28, 2016 4:48 pm

I have this machine, and I measured 6 TPI on the leadscrew. That is consistent with the 6 positions on the thread dial. This could probably be verified from the gear ratios on the change gears, which I would probably do if I was making a new half-nut.

The diameter is about 0.787, which is really, really close to 20 mm. That was measured with calipers, not a 3-wire system, or even gage pins.

Perhaps you could verify that by calling Grizzly tech support. The few times I have talked to them they seemed very helpful.

- Wes

Torch
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Re: Grizzly G9729 Horizontal Lead Screw

Post by Torch » Thu Jan 28, 2016 5:29 pm

Harold_V wrote:Such threads are generally created to standards,
I've heard that some Chinese machine lead screws are not. I think the scenario is something like they designed the machine with metric measurements, but then offer an inch leadscrew option for the US market. So they make a custom lead screw with a metric diameter but an inch pitch.

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LX Kid
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Re: Grizzly G9729 Horizontal Lead Screw

Post by LX Kid » Thu Jan 28, 2016 5:53 pm

Grizzly told me that the lead lead screw was .780" diameter with a left hand 6 TPI. This I already knew. Seems that, doing a little reading, that Acme screws are 29 degrees in pitch. Now all this being said I don't find any taps for sale using this information. While looking around a roughing/finishing tap can run up $200 to $400 depending. Maybe I should just give it up and keep paying the $75 each time I ruin the half nut or it wears out.

Torch
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Re: Grizzly G9729 Horizontal Lead Screw

Post by Torch » Thu Jan 28, 2016 7:26 pm

Or make your own tap out of some O1...

Another option: reduce the wear on the nut.

After wearing out my first nut (similar design machine to yours), I wondered why and found that the slot milled longitudinally left sharp edges where it crossed through each thread. I removed the lead screw and carefully dressed each thread edge with a fine file to dull it.

I also added lead-screw protectors, to keep any chips out.

I'm still working on my second half-nut, several years later.

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WesHowe
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Re: Grizzly G9729 Horizontal Lead Screw

Post by WesHowe » Thu Jan 28, 2016 8:52 pm

James Kilroy posted some videos of a rebuild he did on a vise, which included him making a nut from Delrin by heat forming it around a piece of Acme threaded rod. The heat forming starts in part 4, I included a link below. I know someone else suggested a plastic in one of the other responses. Your half-nut would essentially be making one that way and sawing it in two. IDK how easy this would be for you, but he uses that in a vise where it withstands torque well.

- Wes

https://www.youtube.com/watch?v=7i3NdmtsQYs

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Re: Grizzly G9729 Horizontal Lead Screw

Post by Harold_V » Fri Jan 29, 2016 2:19 am

Torch wrote:
Harold_V wrote:Such threads are generally created to standards,
I've heard that some Chinese machine lead screws are not. I think the scenario is something like they designed the machine with metric measurements, but then offer an inch leadscrew option for the US market. So they make a custom lead screw with a metric diameter but an inch pitch.
Seems I've heard that before, and this instance certainly supports the notion. A true bastard, in other words. So much for Machinery's Handbook, then!

If a guy was so inclined, there's no reason why the thread couldn't be generated single point, assuming it's not too long.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

johnnybar
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Re: Grizzly G9729 Horizontal Lead Screw

Post by johnnybar » Sat Nov 26, 2016 10:26 pm

LX Kid wrote:Grizzly told me that the lead lead screw was .780" diameter with a left hand 6 TPI. This I already knew. Seems that, doing a little reading, that Acme screws are 29 degrees in pitch. Now all this being said I don't find any taps for sale using this information. While looking around a roughing/finishing tap can run up $200 to $400 depending. Maybe I should just give it up and keep paying the $75 each time I ruin the half nut or it wears out.
Just single point some spares.

johnnybar
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Re: Grizzly G9729 Horizontal Lead Screw

Post by johnnybar » Sat Nov 26, 2016 10:45 pm

WesHowe wrote:I have this machine, and I measured 6 TPI on the leadscrew. That is consistent with the 6 positions on the thread dial. This could probably be verified from the gear ratios on the change gears, which I would probably do if I was making a new half-nut.

The diameter is about 0.787, which is really, really close to 20 mm. That was measured with calipers, not a 3-wire system, or even gage pins.

Perhaps you could verify that by calling Grizzly tech support. The few times I have talked to them they seemed very helpful.

- Wes
My G9729 screw measures 0.787"-6 ACME LH single lead also.

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LX Kid
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Re: Grizzly G9729 Horizontal Lead Screw

Post by LX Kid » Sun Nov 27, 2016 7:50 am

Thanks guys for your suggestions and help. I haven't done anything out in the shop for several months due to the heat down here in Tampa, Florida. It has cooled off now and will be back out in the shop soon. I kinda new to machining and have no mentors around to guide me thru machining processes. Most everything I know I got off YouTube or reading and trying. Thanks again and have a Great Holiday Season. Merry Christmas to all! Ron

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