[kNucklBustr]

Have a YCL 11x26 BD lathe. The online manual says 1-1/2"- 8tpi threads. I used a thread gage and came up w/ 8tpi. There is a Chi chuck on it.

But a problem threading a 6" Buck 1-1/2" 8tpi. It wont start on the threads. Seems tight.

Any idea why?

[luv2ride]

How large and what taper is your spindle? Both my 7x and 9x have MT3 with .80" or so thru hole. The 9x has a 1-1/2"x8 thread. I thought some 10x and most if not all of the 11x have an MT4 spindle with a large thru hole, at least 1". If that is the case, I don't see how you can have a 1-1/2"x8 tpi thread.

[luv2ride]

Here is the Grizzly for instance, MT4 with 1-3/4"-8. Still 8 tpi but larger bore.

[hndswthtshdws]

Machinery's Handbook - 7: Measuring Over Wires

[Winnfield]

I had an 11x26 that was 1 3/4"x8tpi. I bought a backplate to mount a new chuck on, and it wouldn't thread on at all. It was because there was an interference in the threads. I took a few thousandths off the back plate threads and the chuck went right on. I didn't mess with the threads at all, just machined the peaks off a tiny bit.

[kNucklBustr]

1-3/4-8 it is. Ill be...

Where do I get a 6" backplate for this? I dont recall ever seeing this size.
I might even purchase a 6" 3jaw w/ reversible jaws if found.

Did some searching- nada.

What have you done or purchased for a 6" 1-3/4-8 ?

My best guess is purchasing a 6" raw plate or 6" 1-1/2-8 plate, fairly common.
Bore out and rethread plate. Lotta work.

1-3/4- 8
Major diameter: 1.7477 / 1.7327
Pitch diameter: 1.6665 / 1.6590
Minor diameter: 1.5989 / 1.5704

1-1/2-8
Major diameter: 1.4978 / 1.4828
Pitch diameter: 1.4166 / 1.4093
Minor diameter: 1.3490 / 1.3204

used this website for thread calcs Theoretical Machinist

[Winnfield]

http://www.wttool.com/index/page/pro...athes+%28WT%29

[kNucklBustr]

This didnt turn out to be a very good purchase from WTTools.
I purchased a 1-3/4-8 back plate and 2-piece reversible 3jaw.

The back plate was 6" in dia. The chuck 6-1/4+" in dia.
I ckd 2 other Chi chucks I have and they are 6-1/4" in dia.

Second the chuck is held together by only 3 slotted screws, less than 1/4 in dia.
Very tinker toy.
My other chucks 6 screws.

And last, the chuck, had the top jaw bolt pocket cut out outside the jaw land, leaving those sharp edges. Not cut out as advertised.

Shars advertises a 1-3/4-8 back plate thats 6.535 in dia.
My past experience is that they never answer questions.

CDCO advertises a 2-piece reversible 3jaw w/ the top jaws not cut out for the bolts. But, w/ those 3 little screws. ugh.
They have answered questions in the past.

My quest continues.

[luv2ride]

I have been looking at the Interstate reversible 4 jaw. I wonder how that one is set up.
It seems to be the cheapest price, does that translate to cheapest quality?

Will WTT take the chuck back?

[kNucklBustr]

WTtools customer service was exceptional. Trying to explain a 6" backplate cant fit a 6-1/4 chuck, thats advertised as 6", was challenging to a non tech CS.

Sending a 8" backplate in exchange.

Personally I believe these chi chucks are the same. Id rather spend the extra for good company support.

[109jb]

The Shars backplate with 6.535" diameter is one that needs machining. The fully machined backplates ar 6.3" diameter. I just went through this for my 6" 3 jaw chuck (6.3" OD), but mine is for a 9" lathe so has a 1-1/2 - 8TPI spindle thread.