Grizzly G0709 threading problems

Mitch Alsup

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When Keith Fenner redid his lead screws, he simply manufactured new ones.......made to fit perfectly, he also replaced 80% of a leadscrew !

The first of a 5 part series:
 

Earl

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Only the threads are worn so I am only replacing the threaded part of the lead screw. The original lead screw is close to 5/8 and I am replacing the threads with 304 stainless. A bit smaller but I have it and I will make brass nuts that will fit inside a newly made steel nut. If I used 5/8 threaded rod, the brass nuts would not fit. I could have made new ones but I am lazy and dont have a gear cutter for it.
 

Earl

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Only the threads are worn so I am only replacing the threaded part of the lead screw. The original lead screw is close to 5/8 and I am replacing the threads with 304 stainless. A bit smaller but I have it and I will make brass nuts that will fit inside a newly made steel nut. If I used 5/8 threaded rod, the brass nuts would not fit. I could have made new ones but I am lazy and dont have a gear cutter for it..
Got the left hand acme reamer today and started on my leadscrew project. If I like how this turns out, I will replace the brass insert shown on the new lead screw with bronze. I had no idea that bronze was so expensive. A 12 inch piece of 3/4 bronze is about $40 to $50. that nut on the left is the one that Grizzly sent me without the mounting screw hole. 40 bucks plus shipping. They are getting that one back.


new lead screw.jpg
 

RDTS

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I have had my Grizzly lathe for 5 or 6 years and have been very happy with it. I changed the motor to 3 phase and added a vfd. It has a dro pros dro with magnetic scales. I mainly use the lathe for chambering barrels for my Benchrest Shooting addiction. I have 4 guns, 3 sporter class and 1 unlimited class that I use in competition. These guns eat barrels at an amazing rate. 1500 rounds (sometime less) and most of them turn into stainless steel tomato stakes. Some barrels will not shoot at a competitive level so they too become tomato stakes. I cut the threads on the barrel to fit the rifle action very precisely. The rifle action is the thread gauge I use mostly. I cut threads until the action fits snugly. (no wobble at all) About a month ago, I was threading a barrel, 1.060 major tenon diameter, 18 threads per inch, 1.023 Pitch diameter (BAT Action) I was using an Arthur Warner HSS stand up threading insert and viper's venom high sulfur cutting oil. The threads were sharpening up so I stopped to check the fit. The action went on about a half a turn. I went in another 4 tenths. The action went on about 3 turns. This is where my problem showed up. I did two more cuts a 4 tenths. My experience with the 416 stainless Kreiger barrels I use is that those last two passes should make the action fit perfectly. I got out my Greenfield ring gage. It would go on 3 turns and stop. At this point I realized that I was not going to get the fit I want and since this was a new barrel blank, (26 inches long) I could cut the tenon off and start over. I called a buddy that is a world class shooter and Benchrest gunsmith. He said he starts his BAT barrels at 1.059. I chopped the tenon down to 1.059 and repeated the process with the same results. I kept increasing the cut until the gage and the action screwed on. They both flopped around on those threads. (There was a lot of wobble - not like it shoud be.) I got out my thread wires and discovered that my pitch diameter was 1.018 ?? My Thread mike said just about the same thing. I did a couple more test cuts on some old barrels with the same results. On a 1 inch threaded tenon, the best that I could do was about 5 turns of ring gage. My conclusion is that I have variations in the pitch. I checked to see if there was end play in the lead screw. There was not. I made sure that the threading tool was square to the barrel. I used a fish tail and visually inspected it. I cut the tenon off of an old barrel and matched up the threads with the barrel in the lathe. I can see some light between some of the thread shoulders. Not much, but some light comes thru on some of the threads. I think that this verifies that the thread pitch is changing. I am out of ideas as to what to check or what the problem may be. I thought that perhaps the headstock to bed alignment was off. I have an Mt3 test bar and an Mt5-ro Mt3 adapter. I measured just under a thou at 15 inches from the spindle with that test bar and the 2 adapters. I believe that the acceptable standard for variation is 8 tenths per foot. I believe that I meet that specification. Any ideas would be greatly appreciated.

I forgot to mention that when cutting threads, both the compound and the cross slide are locked solid. I use a slight amount of carriage brake tension to take up any backlash in the lead screw / half nut connection.
I've had my G0709 for 5 or 6 years also. I have been on the phone with Grizzly and no solutions though they tried to help. I machine the ID (1 1/2") of suppressor tubes 20tpi and the bases for it. I can almost see an imperceptible jump in the feed when threading. I have the same problem as the OP in that everything is fine a few threads in but to go the full length to thread into the tube I have to go maybe 5-10 thou deeper to enable threading the bases in. It's like an invisible change in thread pitch is occurring. This causes my Id to get slightly bigger since I'm using a topper type threading tool. Grizzly just suggested I dive into the gearbox which I'm hesitant to do since my experience with pulling the gears out and fixing a sheared pin in the front gearbox where the dials are. There was no info on how to re index them and had to refer to photos I took before getting into it. Any advice?
 

RDTS

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Doesn't look worn. Like I mentioned to the Grizzly rep the slight jump doesn't happen in the same spot all the time.
Going at it again today on threading the suppressor end caps 20 tpi. When I do my final pass I generally go to the same depth 2 or 3 times. I notice each time it still takes some off (aluminum) but almost at a slight different pitch? It's like it threading at 20tpi one time then 20.001 another time. But it's freaking random. If it was off it should be constant and it's not. I have to go 5 thou more after the cap threads in part way and gets stuck to make it work. Like the OP says was happening on his barrel/trunion threading. I even thread using #1 on the indicator, not the 1,2,3,4 that it says is fine. Freaking frustrating. I'm going to the Jet lathe till I figure it out.
 

JBTEK

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Have you thought about the chain of gears that drives your lead screw -- You have the headstock end gears feeding into the input of the gearbox. Then gears and shafts in the gearbox. If any gear in the drive chain is somehow slipping a bit on its shaft -- that will give you a finer pitch while it's slipping. Is that possible? Could a gear be missing a key, and it's just tight on the shaft but slips a bit here and there? Or something similar?

John
 

RDTS

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Have you thought about the chain of gears that drives your lead screw -- You have the headstock end gears feeding into the input of the gearbox. Then gears and shafts in the gearbox. If any gear in the drive chain is somehow slipping a bit on its shaft -- that will give you a finer pitch while it's slipping. Is that possible? Could a gear be missing a key, and it's just tight on the shaft but slips a bit here and there? Or something similar?

John
Hi John
Yep that's what I'm dreading. Had to go into the front of the gearbox where the threading dials are because a gear pin or key way sheared. That was too much fun as there is zero diagrams or info on re indexing them. Took a few days but got it together, this was a couple years ago. I imagine it's possible that one gear was off a tooth or something that may cause an imperceptible shift down the chain. Was threading today on some 1/2x28 stuff. Everything looked good while I was cutting the thread with a lay down threading tool. Checked the thread with a pitch guage and everything looked good, OD was good etc. But the thread protector just wasnt going on nicely. Had to chase it with a die then it was ok. This kind of **** drives me nuts, especially when you've covered all your bases. Have called Grizzly tech who are great guys but no solution. Even blued the ways, threaded rod etc, looks good. You can still see an invisible jump on the saddle when threading is engaged. So gears somewhere may be the deal.
 

RDTS

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Received the new lead screw and they didn't drill it for the shear pin. Also have the half nuts and they again didn't drill and tap the top half nut for the power feed lockout. What should have been a half day job just got longer. If this cures it (not holding my breath) I think I'm done with Grizzly, I realize their basically an importer but this crap with parts being half done as the OP noted on his part, I'll start looking elsewhere. I had an old Shenwae I picked up used in the 80's for 25 years, no issues. Then a Jet for 10 years, no issues. I realize like my friend Tony from MicroTech Knives said "what do I expect from a $5000 lathe"? Not a ton just more than this.

Update: Replaced the lead screw (drilled it for the shear pin) and the half nuts (drilled and taped for the power feed lockout). Definitely tighter and a bit more force to clap the half nuts, figure it will wear in. Tightened up the cross slide nut so not much slop there. The problem persist on the imperceptible jump but I think I found the culprit. The Wheel for the apron appears to induce a stutter when threading as it comes off the top and gravity causes it to drop. What seems to be happening as I'm threading the table wheel is forced to the back of the gear bar the as it starts to drop it is forced to the forward part of the gear bar with enough weight to cause a stutter. I believe this is causing a variation in my threads. I can tighten the Apron lock nut a bit but from what I read it should be loose. The table takes a little force to move on the ways so I didn't think I should tighten the back gibs on the apron. Any thoughts?
 
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