New To Me, Jet 1336pbd - With Some "issues"

After cutting a 2 1/4 -8tpi thread, for a spider, that didn't fit I took a good look with a 8tpi thread gauge.
Didn't line up. Just a small difference.
This is why I think they just used what was close. Have seen other examples of this in the industry from china.
Have cut hundreds of threads of several styles as well as specials to match weird china stuff over the years.
Ya,these were made in Taiwan but are low end machines with poor fit and finish.
Before I try again I'll be checking everything out as well as the change gears and measuring the pitch closely.
A six jaw chuck, Bison, that I purchased with a 8 tpi backplate fit, but the threads are very loose and it hasn't more than
4 or 5 mating threads.
 
My Polish chuck fits nice and tight. I'm starting to think you and I have different build quality. Maybe Jet was having a bad day when yours was built. Mine does not have poor fit or finish that I have detected. One of the primary reasons I bought this was because of the good things people said about the Jet 1336 PBD. It's not a Hardinge, Monarch, or even a South Bend, but it is better than many of the lesser imports. The worst thing about mine is that it was improperly maintained. That's what I intend to rectify.


Steve Shannon, P.E.
 
Your post does remind me to add thread gauges to my Enco order today


Steve Shannon, P.E.
 
The backing plate will be loose on the threads. The chuck actually will seat firmly against the spindle shoulder so the thread fit is not super critical. I made 2 backing plates for my threaded spindle in 2013 and the 8 tpi setting was accurate on my lathe. I did post a topic on the making of the backing plates.
Pierre
 
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Pulled the chuck off and checked the spindle with a 8tpi thread gauge.
The OB thread is very fat or wide in the OB direction. Just a bit more than one thread or rotation. Will work on that.
Something I had forgotten is it looks as though I need a 23 tooth gear to cut 8tpi.
Had noticed it after failing to get a proper thread and looking for the reason. Since I don't have one, something more to make, I set all such work aside and forgot what I had found at the time.
Now I plan to make the parts and a cutter to get my power hacksaw running so I can cut parts to make a power lap to grind the carbide scrapers and make indicator jigs so I can scrape my
mill-drill and shaper so I can make more parts to........ You get the idea.
The first part I scraped was the lathe cross-slide. Pulled it off and put it on a surface plate. It rocked on two corners. The rest of the machine was no better.
Work done has made great improvements but there's more to be done. When complete, I think it will be a accurate and capable machine.
 
Steve Shannon said:
I might be stupid or I might be hard headed; I guess we'll all know soon! I'm convinced that the headstock gears and pulleys in the Taiwan built Jet 1336 PBD that I have are so nearly close enough to the mainland China built BDB-1340 that I can use the BDB parts to replace the broken bull gear and backgear in my PBD. PDentrum was kind enough to measure his backgear (as well as possible without taking his work lathe apart) and found it to be very close. I was hoping that the Jet parts store would let me return them if I'm wrong. Turns out they won't and they told my local Jet Service Center that the parts won't work. I ordered them anyway. I think I can make them work.
Wish me luck!
Click to expand...

Here is the new backgear, next to the original, which is on the right:
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The differences are:
The new gear is cast iron. The old gear is some kind of steel.
The new gear does not have bronze bushings.
The new gear has a bore which is about 50 thousandths larger diameter than the old gear. I don't think that's large enough for a bushing without boring it out first. Or I could sleeve the shaft the backgear runs on to increase its O.D.
Other than those things I believe the gear will work just fine.
Now I'm eager to hear other's opinions on how to make this work. The options I can visualize include sleeving the old backgear shaft, boring and bushing the new backgear, or turning a new backgear shaft (which is eccentric).



Steve Shannon

eb56c25817a7ff1941be6a8c89202b64.jpg

eb56c25817a7ff1941be6a8c89202b64.jpg

eb56c25817a7ff1941be6a8c89202b64.jpg

eb56c25817a7ff1941be6a8c89202b64.jpg

eb56c25817a7ff1941be6a8c89202b64.jpg
 
8tpi is correct. I was fooled because the outboard thread is thick and a gauge wouldn't sit on it properly. Can't imagine how they machined it like that but there's no indication of distortion.
I used a diamond file and worked the worst of it down. May try to single point cut it at some point but will need to make a gear first.

Steve
If there is no damage to the old gear I would just put in new bushings. Because the eccentric shaft must be worn ? ? I would make a new one. Don't know what material the manufacture
used but some tough material like 4140 pre-hard would be good and would allow a much better surface finish than lower grade steels.
Don't need a mirror finish as there must be a bit of drag to help spin the lube around.
Getting the eccentrics on each end of the shaft to line up might be difficult.
If the gears have wear due to running with bad clearance then the mating gears will also be worn.
I doubt there is any real gear wear and they just didn't lube the shaft. Will need to go back through your thread to see what wear you found in the geared sleeve that
goes on the spindle. Should have at least 1.5 thou or because it's lubed with light grease 2 thou might be better. Its low speed anyway.
Cast iron has better dampening characteristics but I doubt that would be much of a consideration.
 
I agree, not much wear on the old gear, but one tooth on the backgear and one tooth on the bullgear were broken off when I got the lathe. I might have been able to have someone braze in new teeth, but because they are helical I decided I wanted to completely replace them, keeping the original gap tooth gears as spares, just in case. The eccentric shaft may be slightly worn, but not enough to matter (I think??)
Making a new shaft appeals to me in a way, but I'm going to have to figure out how to set it up and center drill it to turn between two precisely spaced axes.
Thanks for your help! I'm feeling my way through this...


Steve Shannon, P.E.
 
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