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Problem threading 4.5 TPI on grizzley lathe

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neil52

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#1
Set up to cut 4.5tpi on lathe correct gear and other settings; made scratch pass, perfect made second pass 1/2 thread off, 3rd pass back to 1st thread etc, grizz. book says use number 1 only[?] I wound up cutting leaving half nut engaged reversing back and got the thread cut but I would like to know what I did wrong. Neil
 

pacifica

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#2
Set up to cut 4.5tpi on lathe correct gear and other settings; made scratch pass, perfect made second pass 1/2 thread off, 3rd pass back to 1st thread etc, grizz. book says use number 1 only[?] I wound up cutting leaving half nut engaged reversing back and got the thread cut but I would like to know what I did wrong. Neil
Probably run some threading tests to see what tpi you are really cutting. I had a lathe threading dial get loose and that caused error. Once tightened everything was fine.
 

T Bredehoft

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#3
Check to see if your compound is at 29.5º or 60.5º. This is often the problem, the compound itself should be about 30º off from the axis of rotation, or the face of the chuck. Less than 45, not more than.
 

4ssss

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#4
I agree, something moved
 

BaronJ

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#5
Hi Neil,

4.5 tpi wouldn't that be an odd numbered thread ?
I must admit when cutting metric threads, I leave the half nut engaged and wind back the chuck. But then again I run the lathe backwards and cut away from the chuck.

Just adding I don't bother with offseting the compound, I go straight in.
 

benmychree

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#6
Hi Neil,

4.5 tpi wouldn't that be an odd numbered thread ?
I must admit when cutting metric threads, I leave the half nut engaged and wind back the chuck. But then again I run the lathe backwards and cut away from the chuck.

Just adding I don't bother with offseting the compound, I go straight in.
4 1/2 TPI is our standard coarse for 2 1/4" diameter (in USA). As an aside, I understand that the Germans have the compound at parallel with the lathe's axis and go straight in and advance the compound towards the cut at each feeding in, this I was told by a German guy who worked in the shop where I apprenticed. I guess there is more than one way to skin a cat ------ For the thread dial, you should be able to use opposite numbers for half threads, quarter threads use one number only, according to info I have seen and my lathes work that way; usually it is even threads on any line or number, odd threads on numbers only, half threads on opposite numbers and quarter threads on one number only, and close anywhere on threads that are a factor of the lead screw, such as if you have a 4 thread screw, you can close anywhere on 2,4,8, 16, 32, etc.
 

blaser.306

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#7
What lathe are you using? I had a similar problem when learning to thread with my 10x22 and it came down to a spacer in the gear train that has to be changed, between metric threads ( normal turning operation ) and "standard " sae threads. The members here helped me thru it and I am certain will do the same now!
 

raven7usa

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#8
On my 4003g lathe, it says to use #1 on the thread dial for 4.5tpi.
 

Mitch Alsup

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#9
On my 4003g lathe, it says to use #1 on the thread dial for 4.5tpi.
You should be able to use any number on the dial, just use the same number for each cut.

But you can always use the metric method::
A) in cut
B) stop
C) back out
D) reverse
E) back in
F) set cut
repeat at A never disengaging the half nut.
 

RJSakowski

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#10
edit: delete "I would agree that something is loose." While it is possible, I don't think you would have returned to the proper setting on the third pass.

Since you were able to successfully cut the thread by leaving the half nuts engaged, I would conclude that the problem isn't in the gear train. That leaves the thread dial indicator. Possibilities include having a misaligned dial, the thread dial gear not fully engaged with the lead screw, or a loose thread dial gear. Your 4-1/2 tpi is a .222" pitch. Being off by one thread on the lead screw would shift the cut by .125" which is close to a half thread.

I had a problem with my Grizzly G0602 where the thread dial was not concentric with the thread dial axle and in some positions, it would the half nits would engage slightly off the mark. This would result in a similar situation as yours. I made a new thread dial which solved the problem.
 
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BaronJ

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#11
You should be able to use any number on the dial, just use the same number for each cut.

But you can always use the metric method::
A) in cut
B) stop
C) back out
D) reverse
E) back in
F) set cut
repeat at A never disengaging the half nut.
Yep, that's just about what I do.
 

neil52

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#12
edit: delete "I would agree that something is loose." While it is possible, I don't think you would have returned to the proper setting on the third pass.

Since you were able to successfully cut the thread by leaving the half nuts engaged, I would conclude that the problem isn't in the gear train. That leaves the thread dial indicator. Possibilities include having a misaligned dial, the thread dial gear not fully engaged with the lead screw, or a loose thread dial gear. Your 4-1/2 tpi is a .222" pitch. Being off by one thread on the lead screw would shift the cut by .125" which is close to a half thread.

I had a problem with my Grizzly G0602 where the thread dial was not concentric with the thread dial axle and in some positions, it would the half nits would engage slightly off the mark. This would result in a similar situation as yours. I made a new thread dial which solved the problem.
I made about 6 lite passes using asharpie between passes trying to see what was wrong; it appeared to be a 2 start thread it measured 9tpi with thread gage but alternated threads each pass. I will check thread dial thanks for the input. like I said I cut the thread leaving the half nut engaged and backing out but it bugs me when I cant figure out why.
 

BGHansen

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#15
Assuming you are leaving the feed reverse lever in place once you are ready to thread. You'll lose registration if you disengage the lever and rotate the spindle.

Bruce
 

neil52

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#16
Assuming you are leaving the feed reverse lever in place once you are ready to thread. You'll lose registration if you disengage the lever and rotate the spindle.

Bruce
my original try was engaging on the 1 on thread dial then disengage back off reengage on the 1; I got the thread cut by leaving the half nut engaged and reversing
 

Mitch Alsup

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#17
Assuming you are leaving the feed reverse lever in place once you are ready to thread. You'll lose registration if you disengage the lever and rotate the spindle.

Bruce
Just reverse the motor (carriage switch), don't reverse the transmission (gear box switch).
 

pacifica

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#18
If you build a swing up toolholder: http://mikesworkshop.weebly.com/swing-up-tool-holder.html cut straight in from the crosslide , reverse motor , use a DRO, there are less calculations to make, less chance of error . you can concentrate on just cutting nice, smooth accurate threads.
 

BROCKWOOD

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#19
My Grizzly is a step down from yours. I have experienced the threading dial loosening off blues. Really cannot fathom how your threads could possibly shift on you when not disengaging on the return. I turned these threads on mine without a hiccup.
 

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BaronJ

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#20
Hi Guys,

I cut this today. 30 mm by 1.25 thread. Cut using my Myford lathe at 200 ish rpm.
Cutting away from the chuck and winding back by hand. There is only about 7 mm of thread.
The material 40 mm round mild steel bar. The hole is drilled 12 mm and then bored out to 1/2" inch.
26-09-2018-011.JPG
 

neil52

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#21
My Grizzly is a step down from yours. I have experienced the threading dial loosening off blues. Really cannot fathom how your threads could possibly shift on you when not disengaging on the return. I turned these threads on mine without a hiccup.
They cut fine while keeping engaged, just had problem cutting in regular mode disengaging then reengaging on the 1 ,it alternated thread each time
 

BaronJ

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#22
Hi Guys,

I thought I had uploaded two pictures, but it won't let me edit my post !
Here is the other pictures.
26-09-2018-010.JPG 26-09-2018-012.JPG
The material I used was salvaged from another project.
 
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