Stuffed around with the lathe today. Wanted to fit a 20mm threading bar to a toolholding block for my qctp. The toolholder has a 3/4" bore and comes with an adaptor for fitting a 16mm or 5/8" bar. You know what they look like. The bar is a Posithread insert holder for screwcutting and is known as a 2020-16 and holds NR16 size inserts. A fairly rigid tool that I like and use a lot. I ended up having to bore out the toolholder on the lathe and finish reamed the bore.
Also toyed around with the concept of a new nut for the compound. I had an idea a while ago of replacing the original spindle nut for an adjustable one, because I have around 005" backlash at the moment. Its manageable because all lathes have some backlash, I just want to minimize it to near zero, so I measured the old one and decided to go bigger in diameter whilst maintaining the height. The reason I went larger in diameter is because I needed space for the adjusting screws and lineup pins.
Here's what I came up with.
Made out of brass with two locating pins pressed into the bottom half, the top has an oil hole which can be filled via a lubing port in the upper slide and also two screws for adjustment. This will require me to fit two more ports on the upper compound slide to access the adjusting screws from above.
As the nut is now 22mm in diameter the existing hole will be bored out to a precision fit (or reamed to match). The edge of the existing hole is too close to the end of the lower slide so a decision was made to offset the hole closer to the toolpost end sufficiently to engulf the original. The idea behind it is to have the two parts move towards each other as enforced by the pins and adjusting screws. This way I'm hoping any wear in the thread of the nut continues to form new thread and maintain its profile. Only one way to find out. If the brass wears too fast it may be a good idea to fabricate a new one out of Acetal (Delrin). There's no way I could have made it with one adjusting screw because the fit in the bore would not allow one side being squeezed tight, it would lockup the assembly.
I'm waiting for countersunk screws to be delivered, the black screw in the pictures won't be used as I need to keep the profile flat.
Here's an update to the nut mentioned above. I counterbored the holes for the pins in the upper nut half. Sufficiently deep to add some springs, for preloading the adjusting screws. The adjusting screws are of different diameters and also pitches.
One is m4 x0.7, the other m3 x0.5, both are countersunk to maintain a low profile. I did this to have a finer adjustment on one more so than the other.
Here's some closer shots.
I still haven't implemented this into my compound as yet, I don't have a milling machine at home.
I've got to do it at work, on the mill there, so hopefully soon. Will keep you posted.