Reply by Ted724

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Posted on Supershop owners

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64 posts in 2192 days

#1 posted 07-27-2019 10:48 PM

The R8 to 4Jt adapter arrived today. There s plenty of metal for the threads, but not sure about the registration shoulder. It s about 1 1/4” at is widest, so don t know if a shoulder of 1/8” around the circumference is enough to properly register a chuck. The Penn State Industries Shopsmith 5/8” smooth bore to 1×8tpi adapter has a shoulder that s a bit under 1 5/8” in diameter.

The adapter seem of decent quality, especially for the price—about $18 with tax.

Here s a photo of the two adapters:

- Ted724

Here are a couple of photos of the R8 to 4JT adapter modified with 1×8tpi threads—

As mentioned earlier there’s not much of a shoulder to register a chuck on the adapter after turning the 4JT end to 1×8 threads, so also used is a “donut” that provides adequate size and heft for registration. The “donut” is a bit over 3/8” thick and with it mounted there are about 1 1/8 of the threads exposed for mating with a chuck.

With a Nova chuck on this adapter (using the Nova “D” adapter for 1×8tpi spindles), I got .005 to .0055 runout on the outside rim of the chuck. I got .004 runout when I mounted the same chuck using a Nova 5/8” smooth bore adapter with my “Shopsmith” 5/8” drill rod spindle in a 5/8” R8 adapter. Don’t know how much runout there would be if the Nova was mounted directly to a lathe wih a 1×8 spindle.

While I don’t think I’ll use it as a substitute for my drill rod spindle with the Nova chucks, it’s a good fit for my 4-jaw independent chuck and the 3-jaw metalworking scroll chuck that are both threaded 1×8tpi. It also gets these chucks closer to the headstock bearing than using the Penn State Industries adapter with the drill rod spindle.

A competent machinist likely could knock one of these out in no time flat, but that’s not me. I feel lucky that I ended up with something that I can use.

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