How does one polish a thread?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

Kernbigo
Posts: 1
Joined: Sun Dec 22, 2013 2:22 pm

Re: How does one polish a thread?

Post by Kernbigo »

When i made thread gages we used to lap them in if they were a few mill over size. We used a piece of oak , about 4" long 1" wide and about 1/4" thick, ground to a 60 deg. included angle. Chuck it up in the lathe with some compound and let it follow the lead.
Mondo
Posts: 1
Joined: Tue Oct 06, 2009 10:24 am
Location: USA

Re: How does one polish a thread?

Post by Mondo »

I can get an impressively good shine on any metal with Simichrome metal polish, a damp soft cloth, and good old fashioned elbow grease. Simichrome is made by German firm Happich. Often found at motorcycle shops, is better than the product from California called Mothers Metal Polish.

A male Acme thread can be polished by making a single fold in a cotton dish towel, chucking the rod in my lathe, applying a small amount of Simichrome to the folded towel and dragging the fold in the thread while the rod turns in the lathe.

SAFETY: Do not wrap the towel around the rod!!! Just drag the fold in the thread. The rod need not be spinning very fast. You can make up a wooden bow from a curved stick to hold the towel so you need not have your hands involved other than to hold the bow. Apply patience generously.

- Mondo
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: How does one polish a thread?

Post by pete »

I've been using Simicrome for years as well Mondo. I first found it in the Brownells gunsmithing catalog. Pretty good product.
Rwilliams
Posts: 1048
Joined: Thu Dec 22, 2005 2:45 pm
Location: Central California

Re: How does one polish a thread?

Post by Rwilliams »

Just recently a friend handed me a paper bag and instructed me to read the book inside at least twice before returning it. When I pulled the book out of the brown paper bag, here was a copy of the Moore book. It has taken me to a different level of how I look at precision surfaces on any machine tool or project I am working on. Just wish I had seen the book when I was starting into machine work long ago. Would have caused me to do many projects differently with better results. A whole new look at precision machine work. Reading the book on the construction of the Mt. Palomar telescope was also an eye opening experience for precision machine work needed for a world class project where no one had gone before.
User avatar
Bill Shields
Posts: 10459
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: How does one polish a thread?

Post by Bill Shields »

As for what you originally asked - the acme thread for an injector...I have to agree with Harold on the pig / lipstick although I usually think purse and sow's ear.

After you have machined a good fitting thread, pack the gland with graphite ribbon and forget about it.

The graphite will flake off onto the thread...

Have you stopped to look at (consider) the INTERNAL thread into which this WORN THREAD mates??

I would be surprised if the wear is limited to the stem only.

Consider how Baldwin originally created the part(s) and I would be very surprised if they were polished. Maybe the stem was ground or cut with a hob, but the internal thread....I would be very surprised if it was done any way but with the equivalent of a tap.
Too many things going on to bother listing them.
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: How does one polish a thread?

Post by Mr Ron »

Mondo wrote: Sun Jul 31, 2016 6:01 am I can get an impressively good shine on any metal with Simichrome metal polish, a damp soft cloth, and good old fashioned elbow grease. Simichrome is made by German firm Happich. Often found at motorcycle shops, is better than the product from California called Mothers Metal Polish.

A male Acme thread can be polished by making a single fold in a cotton dish towel, chucking the rod in my lathe, applying a small amount of Simichrome to the folded towel and dragging the fold in the thread while the rod turns in the lathe.

SAFETY: Do not wrap the towel around the rod!!! Just drag the fold in the thread. The rod need not be spinning very fast. You can make up a wooden bow from a curved stick to hold the towel so you need not have your hands involved other than to hold the bow. Apply patience generously.

- Mondo
I first came across Simichrome back in 1959 when I bought a VW Karmann Ghia. It was supplied with the car and was used to polish the chrome and even the body paint. The finish left after applying Simichrome made the car finish look like a Ferrari. I haven't used it since as I don't have a car that would benefit from it. It's like the pig/lipstick thing. I believe Semichrome doesn't contain any abrasive, so it can't scratch a fine surface.
Mr.Ron from South Mississippi
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: How does one polish a thread?

Post by pete »

Well shiny as nice as it looks to the eye is a whole lot different than what lapping accomplishes despite two threads being done with each method and they might appear to be quite close but they sure won't be. Any thread cut, rolled or even ground on the very best equipment that can be built today will have some measurable amounts of lead and lag error in the thread pitch. It's impossible to not have some and even Moore Tools couldn't do perfect threads no matter how much money they threw at the problem. Polishing only gets you the shiny part. Lapping when done correctly and by someone who has a whole lot more and better experience than I do can help correct and remove some of the threads inaccuracys. Polishing simply can't do that. My best guess is to lap any thread for size and the best accuracy (a micrometer thread for example) would take more than a few trial pieces until you could get repeatable and accurate results.

If I wanted the smoothest running male and female threads possible without that lapping? I think I'd just use a ball screw and nut. Way outside anything Baldwin ever installed on there locos of course. Like others have said Baldwin would have likely just used lathe cut threads and a tap at that size of internal thread. Some parts have a lifespan and it's expected they would just be replaced at some point. Adding some oil once in awhile would go a long ways towards smoother operation and help flush out the wear particles that I'm sure put the most additional wear on those threads. I also think I'd check the compatability and coefficient of friction between that bronze alloy and the aluminum bronze. Some bronze alloys require hardened shafts to obtain the best shaft life. A threaded rod might be even more critical for long life since there's so much more surface area in contact so you'd naturaly have higher wear rates / more contamination to help it wear out even faster.
bill jones
Posts: 38
Joined: Thu Jan 28, 2010 7:20 pm
Location: salt lake city, utah
Contact:

Re: How does one polish a thread?

Post by bill jones »

---Years ago I started polishing threads using convolute wheels.
--this one example shows where I have lightly polished the unused portion of threads on some head bolts---where a nice clean nut now starts and spins on over the full length past the darker area.

---this also works good where the fasteners have been tossed into a bin or a box and get the thread edges burred up slightly.

---the single polished thread photo shows the slight difference between the used threads and the unused threads up closer to the shank.

polished up the sticky thread areas.JPG
Attachments
10 sizes of narrow 12 inch OD convolute wheels.JPG
have 9 different TPI sizes .5x12.JPG
obvious difference in the unused thread area.JPG
Post Reply