Brian H
Super User
That was an AWESOME suggestion...went to my plumbing tool box and got a test piece
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ER40 collet chuck
- Thread starter Brian H
- Start date
Brian H
Super User
Yes, both are identical.
Brian H
Super User
I just tried that. I'm getting 1.556mm now...
Now just to get the gears/pitch issue settled first, are you measuring carriage displacement to confirm the pitch, or are you measuring across 5 threads to confirm pitch? I know it may sound like the same but where I'm going with this is just in case if you are in-feeding uhhhmm... 'different' LOL. Since you are using plastic to test could probably infeed straight in perpendicular to work to eliminate that issue for now as opposed to compound set at angle issues. But just eyeballing what you are showing it does kind of look like the pitch is not mechanically correct for some reason.
I'm just looking over your manual. I assume there must be a mechanical lockout, but any chance you are still engaged in power feed mode, not threading mode & thus 'semi-engaging' the clamshells when you think you are engaged? What is troublesome is you are getting different pitch readings from one run to the next. I could envision reasons why it would not be 1.50mm but it should be consistently the same, not varying.
Longshot, but any chance the lathe can come in metric version? It would not be the first time a metric feed screw was installed at factory or by someone inadvertently. I'm not sure what the IMP pitch should be but we could probably figure it out from the IMP threads it can cut. Typically its 8 TPI (0.125" between threads) or 2mm ~0.078" between threads). But yours could be different.
Have you been threading IMP ok thus far & this is a metric pitch issue, or you are new to threading on this machine?
Longshot, but any chance the lathe can come in metric version? It would not be the first time a metric feed screw was installed at factory or by someone inadvertently. I'm not sure what the IMP pitch should be but we could probably figure it out from the IMP threads it can cut. Typically its 8 TPI (0.125" between threads) or 2mm ~0.078" between threads). But yours could be different.
Have you been threading IMP ok thus far & this is a metric pitch issue, or you are new to threading on this machine?
Brian H
Super User
Attachments
Brian H
Super User
@PeterT I really appreciate the time your taking to walk through this with me.
Here is the setup as I have it. I double checked, lever on the headstock is in the threading position and I have not disengaged the half nut lever since I started the process. I reversed the lathe out far enough to fit my indicator and base in place, then placed a piece of tape on the chuck with a witness mark, then I manually rotated the chuck 5 complete turns and the reading on the dial indicator was 7.78mm(divided by 5 is 1.556).
This is the first thread I am single point threading on this lathe. I attempted to measure the lead screw pitch, but the covers are spring loaded and I don't have enough hands to slide it out of the way to measure it with a scale
Here is the setup as I have it. I double checked, lever on the headstock is in the threading position and I have not disengaged the half nut lever since I started the process. I reversed the lathe out far enough to fit my indicator and base in place, then placed a piece of tape on the chuck with a witness mark, then I manually rotated the chuck 5 complete turns and the reading on the dial indicator was 7.78mm(divided by 5 is 1.556).
This is the first thread I am single point threading on this lathe. I attempted to measure the lead screw pitch, but the covers are spring loaded and I don't have enough hands to slide it out of the way to measure it with a scale
I had the exact same problem you are having with my lathe recently with a 1.5 thread. Turns out the selector fork had slipped and was not engaging the gear inside the threading gearbox. Luckily I was able to put things back into place with a screwdriver through the oil filler hole. Been working correctly since.
@Brian H - I am paranoid of crashing while cutting metric threads because I couldn't disengage the half nut. I previously posted about a method I ran across a while back that allows you to disengage the half nut while cutting a metric thread. I have tried it and it works great.
Thread 'Metric Threading on an Imperial Lathe' https://canadianhobbymetalworkers.com/threads/metric-threading-on-an-imperial-lathe.4616/
It should work on any imperial lathe that has the change gears required to cut metric threads.
Once you get your 1.5 pitch problem worked out, give it a whirl. I think you will love it!
Regarding your pitch problem, it looks to me like your lathe is just not syncing the 127 tooth gear properly.
The 127 gear is usually stacked in front of or behind your gear A, and you have to flip either the bottom or top gear to engage it instead of the other gear.
Your photo looks to me like you do have the 127 gear. It's either the front one or the rear one marked A in the photo you provided earlier.
I found your manual and made copy of the relevant section. Frankly, the description is VERY POOR. It describes selecting the right threading gear but makes no mention of how to properly engage the 127 gear.
Usually on this type of lathe, you "invert" or "flip" gear B in my markup or gear E in the king manual to select which of the two stacked gears of A gets used.
Here are screen shots of the King Manual. Maybe yours is different.
Thread 'Metric Threading on an Imperial Lathe' https://canadianhobbymetalworkers.com/threads/metric-threading-on-an-imperial-lathe.4616/
It should work on any imperial lathe that has the change gears required to cut metric threads.
Once you get your 1.5 pitch problem worked out, give it a whirl. I think you will love it!
Regarding your pitch problem, it looks to me like your lathe is just not syncing the 127 tooth gear properly.
The 127 gear is usually stacked in front of or behind your gear A, and you have to flip either the bottom or top gear to engage it instead of the other gear.
Your photo looks to me like you do have the 127 gear. It's either the front one or the rear one marked A in the photo you provided earlier.
I found your manual and made copy of the relevant section. Frankly, the description is VERY POOR. It describes selecting the right threading gear but makes no mention of how to properly engage the 127 gear.
Usually on this type of lathe, you "invert" or "flip" gear B in my markup or gear E in the king manual to select which of the two stacked gears of A gets used.
Here are screen shots of the King Manual. Maybe yours is different.
Brian H
Super User
I did follow that process. Are you thinking the center gear stack needs to turned around? It doesn't specify that, but it would be easy enough to do and check. There would be some minor change (3 tooth difference) that may be just what's needed...
Thanks for thinking of that. I have to go help a buddy put up a car hoist in his garage this morning, but after lunch I'll switch that around and see what the result is.
@Brian H - If I were you, I'd focus my efforts on figuring out the correct configuration of your 127 gear. It looks to me from your photo (see A above) that you do have it. The difference in the thread pitch that you measure is about right for engaging it or not. Both gears in A are large. And the ratio difference you measure is about right for engaging the wrong one.
Nice that you can just get a length of pipe to test this with. That was a great suggestion! I do similar things with ABS and PVC all the time. Saves using up valuable metal stock.
Looking forward to your comments on disengaging the half nuts while metric threading on an imperial lathe. I love it. But nobody else tried it. Hoping you are the first!
Nice that you can just get a length of pipe to test this with. That was a great suggestion! I do similar things with ABS and PVC all the time. Saves using up valuable metal stock.
Looking forward to your comments on disengaging the half nuts while metric threading on an imperial lathe. I love it. But nobody else tried it. Hoping you are the first!
Basically yes. But I'm not sure which ones are supposed to be flipped on your lathe. It might be the two big ones like you describe or it might be the top gear or it might be the bottom gear. But you have the gist of it. The ratio difference is about right for that to be the problem.
Too bad the manual is so crappy.
The KC–1236 does not come with a 127T transposing gear. They use an approximation with the 86T/91T combo.
I believe @Brian H ’s change gear setup is correct for the required 1.5mm pitch. He also just confirmed that the threading lever 4 is in the correct position.
Therefore either something is slipping (a key missing on a shaft perhaps?) or there is an internal (to the QCGB?) gear mismatch.
I would investgate @Upnorth ’s suggested lead about a shift fork being misaligned. If it happened on his machine, it could be the same problem on Brian’s…
I believe @Brian H ’s change gear setup is correct for the required 1.5mm pitch. He also just confirmed that the threading lever 4 is in the correct position.
Therefore either something is slipping (a key missing on a shaft perhaps?) or there is an internal (to the QCGB?) gear mismatch.
I would investgate @Upnorth ’s suggested lead about a shift fork being misaligned. If it happened on his machine, it could be the same problem on Brian’s…
Proxule
Ultra Member
Food for thought, I printed this out for my lathe, Seems we have the same 12x36 jack ass canada lathe!
7 variations will give you 1.5mm - Handy chart!
Thread pitch settings, sorted by pitch selection, Grizzly G4003 12x36 lathe with 86/91 step gear idler
Thread pitch settings, Grizzly G4003 12x36 lathe, sorted by pitch selection
www.truetex.com
7 variations will give you 1.5mm - Handy chart!
Don't you just love it when they do crap like that! No wonder their manual is unclear. You probably don't flip anything, you just choose the closest approximation.
Gotta wonder if there is enough room there to install a true 127 gear.
Also wondering if the 1.556 is actually their closest approximation to 1.5.......
Nice catch RobinHood.
There's another possibility which showed up on far east milling machines occasionally. As an example imagine the lead screw is advertised as 10 TPI or 0.100" pitch. That would be 2.54mm per turn if my math is working correctly. But suppose instead they installed a 2.5mm pitch lead screw. That's about 1.575 % short. But if their gears are set up to work with a 2.54mm pitch lead screw then you would be out a tad.
At 1.5/1.556 mm = 0.9640102827763496 *100 = 96.40102827763496 %. Or about 3.6 % which is not that great.
So maybe first look at the data sheet for the lathe to learn what pitch the leadscrew is. Then set up the gears to cut leadscrew pitch which is one turn of the spindle for one turn of the leadscrew. Manually turn the spindle N turns and see if the lead screw does the same. The ratio should be 1:1 for the gearing. If its not you know you have a metric lead screw pretending to be something different.
At 1.5/1.556 mm = 0.9640102827763496 *100 = 96.40102827763496 %. Or about 3.6 % which is not that great.
So maybe first look at the data sheet for the lathe to learn what pitch the leadscrew is. Then set up the gears to cut leadscrew pitch which is one turn of the spindle for one turn of the leadscrew. Manually turn the spindle N turns and see if the lead screw does the same. The ratio should be 1:1 for the gearing. If its not you know you have a metric lead screw pretending to be something different.
Good chart. So B-6 with 45-86-60 gears yields 1.5003 = pretty close to 1.50. But still the mystery of why his actual measured pitch deviates significantly.
Maybe try C-2 (on same gear arrangement) & see if it comes out to same pitch.
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That's exactly what I was saying a few posts up. Shockingly, it would not be the first time I've read about a metric feed screw installed on an IMP lathe, despite the IMP dials & everything else indicating it should be IMP. It never rears its head until threading time. Easy for him to confirm - caliper across as many threads as you like, the more the better. Divide measurement by number of threads contained. Then there is the issue of the matching clam shell threads, but first things first.
