# Grizzly G0709 threading problems



## Earl Horgeshimer

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.


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## Mitch Alsup

Have you checked that the leadscrew (and half nut) is prefectly clean and then freshly oiled/greased? (unlikely to ge the issue)

You can verify pitch variation by coating the threads with prussian blue and screwing the action on and off where it binds, unscrew and look for places the blue was worn off. If you can isolate where the cut is mis-pitched you can then isolate where on the leadscrew/half-nut to investigate.

Good luck.


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## benmychree

I'd be looking for wear on the leadscrew.  Barely trace 16TPI on a piece of stock for several inches, then deburr and use an accurate steel rule against the part with the 16th graduation and with a good magnifier compare the two, this should be done in the same axial position where your barrel threading is done. The half nuts should not effect lead variations, nor should lead screw end play (within reason).


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## Earl Horgeshimer

The lead screw and half nuts are clean.  I replaced the thrust bearings at the end of the lead screw and lubed and adjusted them per the manual.
I will blue up the threads tomorrow and see if that shows me anything.  I received a test piece from the action manufacturer (BAT) it is a 2 piece , male and female thread that is the same material and cut with the same program that they use for the action.


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## Mitch Alsup

Did you resolve your macining issue ?
If so, what was the root cause ?


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## Earl Horgeshimer

I have not yet resolved the issue.  Bluing the threads was an unsuccessful effort.  Where the ring gage stopped, the removed blue also stopped.  The 4 threads until the stop all showed contact on the pitch diameter.    I did manage to get the threads to fit very snugly (the fit that I wanted) on the ring gage and the action.  I did that by increasing the depth of cut a couple of tenths at a time until the gage fit.   the problem is that the major diameter when the gage fits, is 1.0556.   The major diameter of the plug gage that I got from the action manufacturer was 1.060. (the specification for a 1 and 1/16 inch, 18 tpi thread)   It also fit snugly on the ring gage.  I checked some old barrels that I chambered on this lathe and they all measured 1.0585 to 1.0595. (digital micrometer) 

I took the lead screw off and inspected it carefully.    No problems.   I checked the half nuts by closing them and shutting off the machine.   With the machine off,  I watched the DRO.  I saw 12 to 13 thou of movement of the carriage when I tried to turn the handwheel.   Pushing the half nut lever down a bit harder resulted in 5 to 6 thou of movement.   $73 dollars later, I have a new set of half nuts and way wipers on the way from Grizzly.
I am not convinced that is the problem.   

In the past,  I use a 3/8  HSS threading tool that I ground.   My threading technique then was to use the compound to advance the cutter.  With the Warner insert,  I plunge straight in.   I think I will re-do this experiment with my old tool and technique.


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## Mitch Alsup

Earl Horgeshimer said:


> I have not yet resolved the issue.  Bluing the threads was an unsuccessful effort.  Where the ring gage stopped, the removed blue also stopped.  The 4 threads until the stop all showed contact on the pitch diameter.    I did manage to get the threads to fit very snugly (the fit that I wanted) on the ring gage and the action.  I did that by increasing the depth of cut a couple of tenths at a time until the gage fit.   the problem is that the major diameter when the gage fits, is 1.0556.   The major diameter of the plug gage that I got from the action manufacturer was 1.060. (the specification for a 1 and 1/16 inch, 18 tpi thread)   It also fit snugly on the ring gage.  I checked some old barrels that I chambered on this lathe and they all measured 1.0585 to 1.0595. (digital micrometer)



I understand about the tight tollerances of benchrest barrel fits.

Are you familiar with the technique told in "Houston Warehouse" where instead of lapping in the threads getting a complete and perfect fit, Virgil put a chamfer on the innermost edge of the action and on the outer edge of the barrel to guarantee that the barrel and the action ended up concentric at both the innermost points and the outermost points of the actioin--and this concentricity was not guaranteed by the threads, but by the champhers ?



> I took the lead screw off and inspected it carefully.    No problems.   I checked the half nuts by closing them and shutting off the machine.   With the machine off,  I watched the DRO.  I saw 12 to 13 thou of movement of the carriage when I tried to turn the handwheel.   Pushing the half nut lever down a bit harder resulted in 5 to 6 thou of movement.   $73 dollars later, I have a new set of half nuts and way wipers on the way from Grizzly.
> I am not convinced that is the problem.



Generally, the half-nuts can have as much as 40-thou and still cut decent threads. {But good luck anyway}



> In the past,  I use a 3/8  HSS threading tool that I ground.   My threading technique then was to use the compound to advance the cutter.  With the Warner insert,  I plunge straight in.   I think I will re-do this experiment with my old tool and technique.



Perhaps cutting on both sides of the carbide tooling is causing the point to drive for and aft and the barrel goes round and round. 
I would try an old barrel using the compound to dial in the cuts.

Good luck.


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## Earl Horgeshimer

I am indeed aware of the exploits of Mr King working the night shift down in Houston.  There are a lot of truths and a lot of myths about what they did.  In my opinion concentricity is important to accuracy no matter how it is done.   At the end of the day, though, I have 3 friends(Benchrest Hall of Famer's) that are of the opinion that it all comes down to bullets, barrels, and wind reading.  Most of the serious competitors make their own bullets and chamber their own barrels - the reason being that they believe that they can do it better than anyone else.  

I really don't believe that the half nuts are bad enough to cause the problem that I am having but that extra push on the lever that reduced the backlash bothered me.   The new nuts will give me the opportunity to pull the carriage apart and see why that happens.

The Warner inserts are HSS not carbide.  I am a little suspect of cutting both sides of the thread at once too.   I have a lot of "drops" from barrel blanks that I can use to practice on.


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## Ken226

Did you ever get this issue squared away?


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## Earl

Ken226 said:


> Did you ever get this issue squared away?


Perhaps.   I decided to go thru the entire lathe.  I replaced the half nuts.   That resulted in some improvement. I found significant "slop" in the leadscrew nut on the cross slide.  That was a combination of Lead screw and nut.  There is a backlash adjustment on the leadscrew nut.  It was already maxed out - came from the factory that way.   I ordered another nut from grizzly and they sent me one that did not have a way to mount it. (no threaded hole to mount it to the cross slide)  That nut was just as sloppy as the one that I have. The cross slide lead screw is very soft and worn.  I can't believe that I wore it out chambering barrels.  I am in the process of chopping off the threaded section of the cross slide leadscrew and replacing it with an acme LH threaded 304 stainless threaded section (1/2 x 10 tpi).  In addition I am making an "anti-backlash" nut similar to the one that Randy Richards did on his you tube channel.  The left hand acme tap will be here this week. The keyway broaches arrived this morning.  I also contemplated getting one of the Precision Mathews 1440 lathes.  A friend has one and I went over and looked at his.   Nice Machine.  The wife said to buy it.  I almost did.  Then I realized that I had made the changes to my lathe that were features that I wanted on a lathe. - I have a 3 phase motor with a VFD for variable speed, a DRO with magnetic scales, a tachometer with SFM calculator.  Aloris tool post, D1-5 set tru 6 jaw Buck chuck with the outside jaws EDM'd off just about flush with the chuck face.  (Modified to hold barrels),  a barrel fixture with d1-5 mount to hold shorter barrels, an inboard d1-5 spider for barrel holding.  All I have to do is fix this problem and I will be happy.  Until then, I am chambering at Bruno's shop.  He has an Enco turn pro.  The only problem there is that his lathe is low.  Makes my back hurt to bend over it.  My lathe is up about 4 to 6 inches off the floor.  Big difference.   I will report some more when I get the nut and feed screw done.

I neglected to mention that I did get some improvement by going away from the "straight in plunge" with the vertical insert tool and went back to the "compound advance" method of threading.   Still had issues with ring gage fit.


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## Mitch Alsup

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:


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## Earl

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.


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## Earl

Earl said:


> 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.


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## RDTS

Earl Horgeshimer said:


> 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?


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## benmychree

Worn lead screw?


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## RDTS

benmychree said:


> Worn lead screw?


Doesn't look worn. Like I mentioned to the Grizzly rep the slight jump doesn't happen in the same spot all the time.


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## RDTS

RDTS said:


> 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.


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## JBTEK

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


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## RDTS

JBTEK said:


> 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.


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## RDTS

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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## RDTS

JBTEK said:


> 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


Unlikely a gear could slip just barely like that. Generally if they shear a key the spin and do nothing.


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## RDTS

Update: Found the problem although the new lead screw and half nuts helped. Nothing about this in the manual. There is a threaded portion in the apron hand wheel that you take a spanner or in my case a needle nose and tighten. First back off the middle setscrew then tighten the large flat threaded portion with your needle nose. Just tight enough that while the hand wheel is turning by itself while your half nut is engaged it won't fall on the downturn because of gravity. After you verify your table isn't lurching anymore because the wheel isn't falling then tighten the middle setscrew. I believe this lurching was screwing up my thread pitch just enough to cause me to have to go deeper on my cut to compensate. The upside is to get to the solution I brought everything else up to speed and the overall machine performs better now. My next lathe will be a good used old American Iron or a Taiwan made one from PM as anything Chinese in my experience  require a good look at and trouble shooting to get the bugs out.


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