Threading on a PM1127 lathe - turning instead of threading

My old lathe was like that. One gear of the pair never got changed. I bet that's what it is.
 
L is the leadscrew. H represents spacers, you should have 2 in the tool box that came with the lathe. Let's say you want 12 TPI.

On the leadscrew you have a spacer, then the 80 gear.

The next spot up is a stack with 50 and 75. With the 50 meshed with the 80 on the leadscrew.

At the top, we have a spacer and a 55. The 55 meshes with the 75 and the spindle. The vertical lines show which gears need to be meshed together.

Get those set up properly, set the gearbox to B, set the thread mode, set the direction. Make sure you use the half nut control, not the power feed.

It's not too bad once you see how it works works, but yes, the chart can be confusing. Always take a scratch pass and verify with a pitch gauge. Particularly if you have a thread on a part you spent a lot of time on.
 
I think H might be a spacer. Look at 8tpi. Power transmission is 60-70 then 60-65. At the top row only Z2 (60T) is being used on the right and to the left in the Z1 position is H. In the bottom row, or L position, only the 65T gear on the right is used and on the left is H. It seems to me H is a spacer that positions a gear on the inside or outside and is not used in power transmission.
 
I would just add to the excellent explanation above that you need to space the gears apart from each other by about 0.0030". Easiest way to do this is to slip a piece of paper between the meshing gears, tighten them in place and rotate the gears to remove the paper. This prevents binding of the gears and possible damage.
 
mikey said:
I would just add to the excellent explanation above that you need to space the gears apart from each other by about 0.0030". Easiest way to do this is to slip a piece of paper between the meshing gears, tighten them in place and rotate the gears to remove the paper. This prevents binding of the gears and possible damage.
Click to expand...

I'm sure using a piece of paper is a pretty common trick in general & is what I do also. After all I learned this when I was 14 as that's what did for my RC cars (back then RC cars had to be fully assembled down to the differentials, no RTRs like today). When I first setup change gears on a lathe I used paper without even thinking about it. Thinking about it now, what do people normally do, just eyeball? Well just eyeball & feel is perefectly fine too I suppose if you know what you are doing. :D
 
I'm somewhat familiar with Change Gears as I have an Atlas 10F with change gears ( I also have a QCGB 42 but that a different story)
and I could be all wet - and if you ask my wife she'll agree.
BUT...
I'm 99.9% sure the gear train is almost all double gears that fit together.

X is the Shaft the gears mount on.

If you look at the Picture Z1 / Z2 -( Z1) is a bold line as if you can see it's outline so it would be on the outside on top of the Z2 gear.
Z3 / Z4 - the (Z3) Gear is shown with a fine/lighter line as if it is behind the Z4 gear on the inside.

I would guess that "L" is the leadscrew shaft and is identified with a gear and a specific number of teeth.

If you follow the columns in the chart the for the .07/mm pitch it would be:
Top Shaft:
Z1 - Outside Gear 45 teeth
Z2- Inside Gear 75 teeth

Lower Shaft:
Z4 - Outside Gear 80 teeth
Z3 - Inside Gear 20 Teeth

Gear on Lead Screw Shaft - 85 Teeth

The "H" I'm not sure But my guess would be the BELT Position but I would have to pull down and read the full manual.

Good luck.
 
I agree with ttabbal that H must be a spacer & L means leadscrew. I don't have this lathe but my lathe is the same way, I have a spacer for the gear that drives the leadscrew that I need to reorient for metric threading. My chart doesn't show a letter or anything, it's just blank where the spacer needs to be.

I was trying to think of a word like that starts with the H sound in Chinese but couldn't find one. I came to the conclusion that whoever wrote the manual must have a heavy accent & decided to name it Hempty. :big grin:
 
I don't see how "H" could be belt position. Changing the speed of the spindle doesn't affect the pitch or feed. The only way a belt could affect pitch is if it was inserted into the gear train but slippage would make it impossible to synchronize the spindle with the leadscrew.
 
H probably stands for "holder" as in placeholder
Could also mean hellish
I notice two slightly different charts for inch threads- did the mfg offer an inch or metric machine and PM only sells the inch version?
 
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