Machinists - I need help with threading jig

[Jim Underwood]

Not wanting to spend $300+ I decided I'd make my own threading jig taken from Jean Michel's plans.

So I bought some 3/4x16 threaded rod, some matching nuts, and a spindle adapter to adapt from the 3/4 up to 1x8 spindle size.

I built the jig from scrap 3/4 ply and got the threaded rod mounted and trued up pretty well, and got the cross slide working. Then I mounted the spindle adapter...

And that's where I'm stuck. The adapter wobbles on the 3/4 rod pretty badly. It's so bad it's not possible to use.

Here are the things I've tried to get the adapter to run true:

1) I've faced off the end of the rod as true as I can get it, and seated the spindle adapter all the way down.
2) I've placed a nut on the rod, then screwed the adapter down til it meets the "lock" nut, hoping that would give it something square to seat on.
3) I've rotated the position of the nut and adapter to all points around the rod, until I minimized the amount of wobble. It's still unacceptable.

At this point I'm wondering if it's the adapter, the rod, or the nut, or all three. I'm not sure what to do next.

help?

Not shown is my homemade cutter. It would normally mount in a small jaw chuck where the scroll chuck is now and run at 3000 RPM. It cuts fairly well, but the wobble of the spindle adapter prevents a good test.

[Bruce Page]

Jim, it’s hard to say exactly what’s going on but I’d guess that you have a considerable amount of play between the allthread, spindle adapter, and nut. Big box threaded rod and nuts aren’t made to very close tolerances. I suspect that the adapter and the nut are cocking when you tighten the two together. I’m not positive that this will work but you might try adding a second nut and tightly jamming the two nuts together then tighten the spindle adapter against them. If that doesn’t fix it, try to somehow square up the outboard face of the nut perpendicular to the allthread axis.

[Paul Douglass]

Man I can't help you, but when you get it all figured out, how about a set of plans? I been thinking on something like that. I have a tap to make threads but so far I have not had any luck getting a good streight tapped hole. Need a jig. Like the handles you made also.

Sorry, I didn't read your post correctly. Where did you get Jean Michel"s plans?

Thanks

[Matt Hutchinson]

I haven't built one of these, but I know that you don't want ANY wobble. You have saved so much money to this point, maybe it's worth paying a machine shop to thead the end of a rod, with a shoulder to screw things against.

I know it's not ideal. Just a thought.

Hutch

[Paul Engle]

All thread rod is made from a wire ( not bar stock) the size of the thread so it is not " machined " so to speak but stamped and rolled . unfortunatly this means a lot of slop as the spec for the rod and nut only calls for the larger % of the root to match , they are not meant to be precision in any way, only to tighten up with out slipping. They will not register properly but " cock to one side" you will need a machined specific rod and nut to remove the slop and have the nut present square to the rod and the holder, plus a method of tightening the whole thing up to make fast and solid. Making the spindle precise ( square to the chuck) out of this is a real challenge and I recomend a machine shop make it for you or some one with a metal lathe and mill.I am current building an ornamantal turning device for my Jet and have mounted the spindle ( threaded 1"-8 TPI Stainless Steel bar stock ) in a 1 1/2 ID chrome molly tube which is mounted in a set of ball bearings and all mounted in a block of T-6 aluminum which mounts like a tool post to the cross slide ( Hardinge tool makers slide) which mounts on the bed of the lathe via a 1 " thick aluminum plate. phew... so you see in order to cut accurate threads you need near precision spindle or at least one as accruate precise as the spindle the chuck is mounted on , etc , if you want to use the jig. .... or you can hand cut em with the hand tools avail in any turners catalog.If you try to mount all this on wood .... it will never repeat accuately and you will not be able to align the spindle to the chuck ( on 3 axis's , x,y ,z) good enuf to get the thrds to work properly , you will be frustrated trying to get it to work accuartely from hour to day as the humidity changes, the wood compresses , etc.

[Fred Conte]

Jim what the folks have already said about all thread is very true plus it is rarely straight.

But here is a simple solution that may or may not work...

Take a 3/4" washer and drill 3 holes 120 degrees apart on a circle smaller in diameter then your adapter. Tap the 3 holes for 1/4"-20 bolts, either hex socket head or set screws and a nut for each. Tighten the small adapter against the washer and nut and adjust the three 1/4-20 screws until there isn't any wobble or it's minimized, then tighten the three 1/4-20 nuts to the washer so the screws won't move.

I hope you understood what I have tried to explain, if not pm me and maybe I could send a drawing:).

HTH - Fred

[Bob Vallaster]

Paul,
Here's the link: http://www.atbq.qc.ca/jm2/
Browse the whole thing. It's worth the time to see it.

Bob V.

[Jim Underwood]

Fred,
Excellent idea. I didn't follow it totally the first time, but got the gist of it. I'll think about it some more and I'll get it.

[GLENN THOMAS]

I have also given some thought to making a thread cutting jig as well but didnt know how to make the cutter or where to buy one. Could you post some pictures of yours?

Thanks
GT

[Paul Douglass]

Paul,
Here's the link: http://www.atbq.qc.ca/jm2/
Browse the whole thing. It's worth the time to see it.

Bob V.


Thanks Bob

[Jim Underwood]

I'll post a pic of the cutter at some point. Not tonight though..

It's nothing special, just some cold rolled steel chucked up and faced off with a scraper, drilled and tapped, then bolted a piece of air hardening strap on. I then spun it in the lathe and ground it with a die grinder till I got a circle, then chopped notches in it with the grinder...

I'll try to make a better one after I get my wobble solved.

[Scott Hubl]

Hows this coming along Jim?

[Pete Jordan]

Hey Jim,

Quite a few of the guys in our club have built these and they ended up ordering the threading head from http://www.bestwoodtools.com/ for $119. They said the there was too much run out with standard stock. I have the parts but not the time to put mine together

[Jim Underwood]

Hows this coming along Jim?


:(

It's not. I shelved it. I haven't gotten out to my machinist friends place yet.

[Norm Zax]

What makes the cutter advance at a specific angle? Is it the angle at which the cutter is created? Is the cutter plane exactly perpendicular to the spindle axis or slightly off, causing the cutter to dig in at an angle and thus create a specific TPI ratio?

[Jim Underwood]

The workpiece is advanced and turned at the same time because it is mounted on a threaded rod and "screwed" into the spinning cutter. No angle is necessary since the only thing contacting the work piece is a small arc of the cutter.