Can I turn a part from hard clear plastic?

[cazclocker]

A very good first attempt. It looks like your order of operations is good. A couple of thoughts/suggestions:

Finish is outstanding! Is what is in the photos after polishing?

It looks like you tried to part off the excess length of rod; with that much stick-out and Acrylic being somewhat brittle, I would saw of the short end and just clean up the saw cuts by facing (which you did anyway).

To get the knob to seat fully on the shaft you have two options: undercut the "glob" so that it is smaller than the root diameter of the threaded portion or drill/bore the end of knob deep enough so that it fits over the unthreaded portion of the shaft (that's what I would do, since you're drilling & tapping anyway).


Keep up the good work!

Thank you ChazzC.
Order of operations.... what makes me question my order of operations is that I'm now wondering if I began forming the wide diameter close to the chuck first, instead of last. I don't know. I'm not very experienced with thinking things through, so maybe the way I did it was OK.

Your second paragraph - do you mean saw off a piece of the rod before I chuck it up, instead of the way I did it? If that's what you mean, I think it makes sense. I'm not sure why I did that. I wasn't prepared for how messy this material is!

As far as fitting the knob all the way to the runner's shoulder: I'll likely have to implement your first recommendation... undercut the "glob" so that it's smaller than the thread's root diameter.

 

[cazclocker]

Chuck up the runner and turn that blob down to just below the height of the thread crests. Then, be sure to counterbore the next knob to be able to screw all the way to the runner shoulder.

I wish I could chuck up the runner! Unfortunately the only lathe I have is my little Rivett 2b watchmaker's lathe, and material insertion into the chuck is limited to the chuck's physical construction - there's a solid wall in the back!
That's why I say sometimes I wish I had a Myford Super7 or a Schaublin or some other larger lathe that will let me turn longer material. Ah well, I'll figure out something. I'll likely use my Foredom tool with a diamond wheel.
I'll figure out something... it will take me a while, but knob #2 is coming.

 

[Boswell]

you could just hand file the blob. I doubt it would take very long. Or as others have suggested, counterbore the base of the knob to accept the larger diameter.

 

[tq60]

Place a nut in the chuck then thread the runner into the nut.

Wait...place double nuts on runner so you can lock them, then place into chuck.

Slow as it can go and make some sort of bushing to support the end in tail stock and just remove the high spots.

If you have a cheap die you can face off the opposite side from the start side so that a cutter is flush with the face then use it to cut threads to shoulder.

Counter drill if needed but drill this FIRST.

Before drilling the to be tapped hole so you can control the cut better.

Drill counter bore

Drill and tap thread

Test fit.

Face until depth perfect then continue.

Sent from my SM-G781V using Tapatalk

 

[Firstram]

How did you polish the finished part?

 

[Just for fun]

Your first attempt looks pretty good, I like the finish. Looking forward to your next attempt.

 

[cazclocker]

How did you polish the finished part?

The only part that is polished is the rim of the larger diameter (the part that I cut the convex radius on). I polished it with 3M wet/dry sandpaper. I used the following grit sequence: 300 - 500 - 800 - 1,000 - 1,200 - 1,500 - 1,800 - 2,000 - 3000.

 

[wachuko]

First attempt came out great!!

But I agree, no need to modify the shaft to remove that high spot... Instead, why not manually remove the material from the knob to clear that and be able to thread it all the way in? Using a end mill on a holder and just take it slowly, by hand, to remove the material from the knob...

I know you will make another one... but seems like that one can be saved...

 

[cazclocker]

First attempt came out great!!

But I agree, no need to modify the shaft to remove that high spot... Instead, why not manually remove the material from the knob to clear that and be able to thread it all the way in? Using a end mill on a holder and just take it slowly, by hand, to remove the material from the knob...

I know you will make another one... but seems like that one can be saved...

You make an excellent point. But, I've decided to file down the weird metal glob at the base of the TS runner's threads. Part of what spurred me on to do that was remembering something... I have a steadyrest for my little lathe! Long story, but it's been a while since I've done much with my Rivett 2b watchmakers lathe, so I'd forgotten what accessories I have.

I'd rather get busy making another knob, but the crapped-up tailstock threads are bothering me - so I set up the tailstock in my 4-jaw and used my steadyrest for support on the other end. As you can see, I put a short sleeve of "hobby brass" around the tailstock to prevent any damage. One drop of oil and it rides like a beast!

My time today was limited, so here's what I've got so far...




More tomorrow...