Metric or imperial lead screw on my 10 x 20 lathe

[Laz]

I do have a complete set off Gears to many to list. the Manual originally said CQi628 Bench lathe, gut they put a sticker over that and called id a Precision 3003-0005. I have figured out that the gear box can be set 1 to 1 or 1 to 2. What is throwing me is the someone said if it does not come with a 17 tooth gear it may not be a imperial lead screw. This is one I found online that is exactly like mine. no mention of the lead screw. It just says you can cut both imperial and metric. I do plan to go directly to adding the ELS, I have all the gears but they are a real pain.

 

[brino]

Better than using a ruler and counting threads (at least with my eyesight!) is to use a thread gauge like those pictured below.
Try to get ones that cover the widest range of BOTH imperial and metric threads.
They do not have to be expensive, and the will get used a lot for identifying random threads in your shop.



The problems with relying on the existence of a 127 tooth gear are:

1) a lathe could use something else.......
The 127/100 (=1.27) gear tooth combination gives exact metric-imperial conversion, however other combinations are so close that for short threads of only a few inches, they are close enough. These "close enough" ratios include:
47/37 = 1.27027027027
80/63 = 1.26984126984
56/44 = 1.27272727273

2) the combination gears to do the metric/imperial conversion could be hidden within the quick-change gear box..... they might not be in the pile of extra change gears that you swap in/out.

Brian

 

[markba633csi]

I think your leadscrew could be metric. What is the outside diameter?
Checking my pocket ref the only imperial 12 tpi size would be 9/16" -12 tpi in the National coarse standard- if your screw is 9/16" diameter it could be that one, but
there are several 2mm metric sizes which would measure 0.945" for 12 threads worth and at first glance they might look like 12 tpi

 

[RJSakowski]

I think your leadscrew could be metric. What is the outside diameter?
Checking my pocket ref the only imperial 12 tpi size would be 9/16" -12 tpi in the National coarse standard- if your screw is 9/16" diameter it could be that one, but
there are several 2mm metric sizes which would measure 0.945" for 12 threads worth and at first glance they would look like 12 tpi

The Grizzly G0602 lead screw has 3/4" 12 tpi L.H. thread. The o.d. measures .7914"/20.10mm.

 

[RJSakowski]

If you are planning a sooner rather than later ELS conversion, it really doesn't matter much whether the lead screw is Imperial or metric. The software will account for it properly.

The picture that you posted looks more like the G0752, the variable speed version of the G0602. The thread dial doesn't look like the 602/752. Some close ups photos of the back end and the face of the headstock would be helpful. new C6128 lathes are a different critter than the one pictured. I wasn't able to find any info for CQi628 or Precision 3003-0005. You can download a user manual for the G0602/0752 lathe from the Grizzly website. It should help you in identification if it is indeed a clone of a Grizzly.

 

[Laz]

here is the thread chart that is on the front of the Late. I have used a tread gauge and it shows 12 TPI on the lead screw and my gear box can be set for 1 to 1 or 2 to 1 . So I think am OK for the Conversion. The manual is useless and the chart on the for t say "For metric Lead screw. I do not think 12 tai is metric . to add to the confusion, under the specs in the manual it show this,

Metric thread. 0.4-2.5 mm
number of pitch. 12
Imperial thread. 8-35/in
Number of Pitch. 15

If you can make sense of all this . I cannot

I figure if the lead screw I have is 12TPI (which by every measurement I can do) . and the gear box lets me do a 1 to1. or 2 to 1 I should bet able to do the ELS Cough42 conversion.

Once agin thanks for everyones help.

 

[RJSakowski]

You should have no trouble with the Clough42 ELS conversion. What matters is what is the encoder rpm relative to the spindle rpm and encoder pulses per rev., what is the stepper rpm relative to the gear box input rpm, the gear ratio in the gear box, and the lead screw pitch. These can all be accounted for by adjusting various parameters in the software.

I run my gear box at 1:2 (for higher torque) and my stepper ratio at 1:1. My encoder is running at 1:1 with the spindle and set my lead screw pitch at 24 tpi to account for the gear box ratio.

To understand what is happening with your lathe, one needs to know what is going on with the two "black box" rectangles in the diagrams. Uo cut a 12 ti thread with your lead screw, the lead screw need to turn at the same rpm as the spindle. From the Imperial chart. the F and G gears are 80 and 60 respectively. The reduction in rpm by gear train (not including the black box) is 40/80 x 80/60 x 75/50 = 1. If the gear box is et for a 1:1 reduction, then the spindle black box would also be a 1:1 reduction. This is easily verified by counting teeth or measuring the o.d. of the gears of the spindle black box and rotating the lead screw input shaft while observing the lead screw rotation when the selector levers are set in the BII positions.

Since a 127 tooth gear is not used for transposing, other is an approximation being made for either the Imperial or the metric thread. Given that you measured 12 tpi, the 2.1666 mm pitch isn't a nice round number and I would expect the the transposition is from Imperial to metric. Looking at the various metric thread gear combinations, it appears that the metric approximations are not very close at alll so converting to an ELS would be a wise choice.

 

[Laz]

You all are way smarter than I am on this, and your help is great. I will check the diameter of the lead screw. I was not aware that would make a difference. I have checked the TPI using the carriage and seeing how many turns of the lead screw are made in a inch and I will check it in 5 inches ( I figure any oddities will show up over a longer range). I will also get more pictures.

I do agree that the cough42 software will work with either metric or imperial. My concern was the internal;; gear gauge box. In the BII position it appears to be one to one.

 

[RJSakowski]

You all are way smarter than I am on this, and your help is great. I will check the diameter of the lead screw. I was not aware that would make a difference. I have checked the TPI using the carriage and seeing how many turns of the lead screw are made in a inch and I will check it in 5 inches ( I figure any oddities will show up over a longer range). I will also get more pictures.

I do agree that the cough42 software will work with either metric or imperial. My concern was the internal;; gear gauge box. In the BII position it appears to be one to one.

The diameter of the lead screw doesn't make a difference. The pitch is what matters. I offered the o.d. as another data point. It appears that your lathe is significantly different from the Grizzly lathes. Whole the same basic style was used for many different brands, there are enough differences that they should only be used as a reference when comparing.

The gear box will not be an issue. There are multiple ways to compensate for that gearing when setting up the software for your machine.

 

[Laz]

Thankks RJ.

I agree it is only similar to the Grizzly. I have checked the lead screw multiple ays and the screw appears to 12 TPI. This Lathe was probably intended for the European Marked. The Chuck system is one they use in Germany. I like it because it is not screw on. I found backing plate blanks at precision Mathews. One of their imports must use the same system.

I have all the ELS parts now. It will take some time to figure out how to load the software etc. I use Apple, but James said it should not be a problem. The outer issue with this Late is the Idler arm for the pully belts is in a different place so I may have to mount the Servo meter outside .

Thanks again.

Mike