4 Lead Helix Help

Rogue_Machinist · Sep 3, 2020

So since I work in a job shop we get all sorts of weird jobs. However this job im working on seems easy but also since we dont have proper tooling I need help.

A customer brought us a deli slicer adjust job and shaft. The knob is stripped out. I need to cut a 4 lead helix, NOT an acme. I tested several acme inserts and they just dont fit.

Is it even possible to cut a 4TPI quad lead helix on a lathe? I am unable to post photos as I have no service at the shop. The customer doesnt wanna spend anymore than $200 to do this job. I will provide photos once I get home.

We only need to make a collar for the shaft. However there is no tooling in my shop to make such a cutter small enough to get into a .550 hole +/- .010" with a deep enough tool tip to get the bushing.

magneticanomaly · Sep 3, 2020

If it is the nut you need to make, I would mold it out of epoxy, right on the screw.

You could add graphite powder to the epoxy to lower friction. I would experiment dipping the screw in molten wax before molding as a release agent, also to get a little clearance. If you dip stone-cold screw in wax, layer may be too thick..that is what i mean by "experiment..wax at different temps, screw at different temps. MY first try would be with cold screw and very hot wax.

$200 is pretty cheap for a tricky one-off. What wil the customer do if they CANNOT get a new unobtainium knob for $200...Buy a new $5000 slicer?

Rogue_Machinist · Sep 3, 2020

magneticanomaly said:
If it is the nut you need to make, I would mold it out of epoxy, right on the screw.

You could add graphite powder to the epoxy to lower friction. I would experiment dipping the screw in molten wax before molding as a release agent, also to get a little clearance. If you dip stone-cold screw in wax, layer may be too thick..that is what i mean by "experiment..wax at different temps, screw at different temps. MY first try would be with cold screw and very hot wax.

$200 is pretty cheap for a tricky one-off. What wil the customer do if they CANNOT get a new unobtainium knob for $200...Buy a new $5000 slicer?

Well Pennsylvania, especially the area I live in, is poor. So a new Slicer might be in the works for him.
And yes im fully aware $200 is pretty tricky. But my boss seems to think its just easy to make a custom ID threading tool. And I think I have an idea to fix it for the customer. Make a brass collar with 4 pins pressed in @90° intervals which could allow it to "thread" onto the shaft. And then just epoxy the brass collar into the plastic knob. Just an idea.

1953chevB · Sep 3, 2020

magneticanomaly said:
If it is the nut you need to make, I would mold it out of epoxy, right on the screw.

You could add graphite powder to the epoxy to lower friction. I would experiment dipping the screw in molten wax before molding as a release agent, also to get a little clearance. If you dip stone-cold screw in wax, layer may be too thick..that is what i mean by "experiment..wax at different temps, screw at different temps. MY first try would be with cold screw and very hot wax.

$200 is pretty cheap for a tricky one-off. What wil the customer do if they CANNOT get a new unobtainium knob for $200...Buy a new $5000 slicer?

To keep cost down this probably the only way, or maybe 3D print a nut, draw it up and print it

Hardplates · Sep 3, 2020

I can think of 4 ways off the top of my head to make such a part, none of them are under $200.

Usually when a customer puts a price cap on a job I send them elsewhere

Booze Daily · Sep 3, 2020

I was going to suggest the dowel pin method. I’ve done it before and it worked for the application.

If they torque on that knob you might want to think about 8 pins.

Dan from Oakland · Sep 3, 2020

make a ring, tin the id and pour some babbit around the shaft. Makeup a little fixture to center things up, smoke the screw and cast the nut.

Phil in Montana · Sep 3, 2020

Pass up the job $200 is chump change for all the setup you will have to do, dont think I would want the job at $500...Phil

Nerdlinger · Sep 3, 2020

Can you buy one of these $20 knobs, bore out the inside to the OD of your shaft and then cross drill and tap for four cone-point set screws to bite on the root of the shaft thread?

Clamping Knobs, Six Arm Grip, 3/4"-10 Thread Size

McMaster-Carr

Rogue_Machinist · Sep 4, 2020

Nerdlinger said:
Can you buy one of these $20 knobs, bore out the inside to the OD of your shaft and then cross drill and tap for four cone-point set screws to bite on the root of the shaft thread?

Clamping Knobs, Six Arm Grip, 3/4"-10 Thread Size

McMaster-Carr

I think the customer is trying to keep the adjustment increments on it. I was gonna just search a few places I know that have outdated appliance parts like that. But the owner is just seeing dollar signs.

Street · Sep 4, 2020

i tend to like the white metal method as i have done a few whitemetal bearings before.
Your going to need to soot the shaft fairly heavily, i think it will be trickier with a thread, especially the sides of the thread.
Just thinking if it near the food any lead in it will be a no no so a tin based babbitt will be better.

Yes if the depth of tool will fit you can screw cut it...it will be still tricky as if it does not fit you have four or more points to look at to determine which feature is the issue and sorting that out could easily blow $200 spend.
I have done 2 starts and if your good with demensions its no big deal, four is just double the effort.

Mike C. · Sep 6, 2020

I wouldn't do that in my home shop for $200. Make a screw, maybe. Make a 4 lead nut with a custom thread profile, having to figure out the cutter and probably scrap two trying to make it work? Nope.

Gordon Heaton · Sep 6, 2020

I can't help you with the job, but I'd sure like to see how you solve the problem. Take lots of pictures too, please!
I would attempt it in my home shop, time permitting, because win or lose it would be a valuable learning experience. And I just like helping people out sometimes.

dalmatiangirl61 · Sep 6, 2020

Why is it a 4 lead screw? Does it have to remain a 4 lead screw? Why not just replace screw and nut with plain acme?

LexD · Sep 6, 2020

dalmatiangirl61 said:
Why is it a 4 lead screw? Does it have to remain a 4 lead screw? Why not just replace screw and nut with plain acme?

It's not actually a 4 lead screw, it has only one lead, that being one inch but it has 4 starts which allow 4 times more movement per revolution than a single start thread of the same pitch. I think in this application it was designed that way for fast adjustment.

dalmatiangirl61 · Sep 6, 2020

LexD said:
It's not actually a 4 lead screw, it has only one lead, that being one inch but it has 4 starts which allow 4 times more movement per revolution than a single start thread of the same pitch. I think in this application it was designed that way for fast adjustment.

I was thinking fast adjust would be the answer, question how critical need would be for fast adjust, its a meat slicer. If it just needs to remain adjustable, I would think acme would work, sell it as finer more precise adjustment.

Rogue_Machinist · Sep 8, 2020

So we spoke to the customer over the weekend and they do need the fast adjustment. But also want to attempt to keep it as original as possible. So I quickly ground an old cemented carbide tipped bore bar into the profile of the shaft thread. used a headstock stop and 4 jaw in a 3 jaw. Just gotta finish the cuts to size in morning. But did it for $300 which the customer agreed to on the price.

Rogue_Machinist · Sep 9, 2020

I didnt get a chance to take a photo of the finished bushing as the customer was waiting for the part. But here is the completed assembly.

1953chevB · Sep 9, 2020

nissan300ztt said:
I didnt get a chance to take a photo of the finished bushing as the customer was waiting for the part. But here is the completed assembly.
View attachment 298931

well done job completed

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