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elf
11-01-2012, 03:42 AM
Here's an image of the M6x1 stainless steel all-thread rod I'm going to use for a leadscrew in a small project. I'll be making the nut using the technique here. (http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way) I'm really only concerned with making the threads smooth, not making them more accurate. Plan A is to use a cast polyurethane nut, 60mm long, and valve lapping compound, 120 and 280 grit. The length of the leadscrew is 350mm. I'm not sure if the polyurethane can handle the heat created by the friction from lapping. Has anyone tried this? Is there a better way to do this (inexpensively)?

http://img.photobucket.com/albums/v649/etfrench/PMax0262-0435fs.jpg

Note: Magnification is 7X. The image was created from 156 individual images by focus stacking with Zerene Stacker.

Boucher
11-01-2012, 08:06 AM
When single pointing threads, I have always used the cratex sticks. I keep four grades on the shelf above the lathe.

http://i109.photobucket.com/albums/n50/boucherbyron/IMG_0266Small.jpg

They improve smoothness and appearance significantly.

Dan Dubeau
11-01-2012, 08:25 AM
Quick and dirty way of trying it out would be to tap an m6 hole in a small scrap of aluminum, or brass. Cut a slit with a bandsaw, or hacksaw inline with the hole to split it. Now just throw some lapping compound in there, and close up the slit with a vice, of c clamp to apply some pressure. Clamp the block in a vice, and run the rod in and out while chucked in a drill. add some tension every pass or so. Should work to clean up the threads.

ikdor
11-01-2012, 08:50 AM
Byron, for the unwashed among us, what kind of grit would be sensible for the cratex sticks?

Elf, that is an impressive picture indeed.....

Igor

big job
11-01-2012, 09:29 AM
I have in the past done that, as Dan said, but, I cut one side of a nut, held with vise grip
and the threaded rod chucked up in lathe using valve grinding compound I simply ran
the lathe for.&reverse worked well. Then to the buffer. Thats if you have a lathe that
will reverse. I should say I started with the nut just held in vise grip then a little more
pressure on the grip until a nice surface. Or a drill.

Ian B
11-01-2012, 10:11 AM
Elf,You say it's allthread - is this a length that you bought / acquired? It looks to be far rougher than I'd expect - run that through your fingers, and you'd get them shredded. Would it be worth starting out with a better piece of allthread?Ian

Black_Moons
11-01-2012, 10:58 AM
Damn nice pic, you must have quite the rig to be able to take 150~ photos from the same position. (And to make it pratical to do)

wierdscience
11-01-2012, 11:03 AM
x's 2 for what Dan said,you could even use blocks of hardwood or fiberglass for the slip laps.

Boucher
11-01-2012, 11:28 AM
Igor, I have 120,240,320,400. The 120 and 240 are the most useful.

Mcgyver
11-01-2012, 11:51 AM
that's horrible looking stuff....I don't know that I'd accept it....but maybe it was free or you've had it forever

anyway, to one of your questions, the amount of heat generating by lapping is a result of speed; if you want less heat so you don't melt the plastic lap run it more slowly. imo you won't be able spin it too quickly if its any length anyway as you have to worry about whip

the worst areas seem the edges of the crests. I'd try first with a stone held at an angle then finer and finer emery cloth wrapped around wedges of hardwood. protect the bed

elf
11-02-2012, 03:53 AM
The stainless all-thread was from a local hardware store specializing in screws. It's main redeeming qualities were cheap and available now :) It's going into a prototype, so if the concept works well, I'll be able to easily replace it with a higher quality screw. Metric trapezoidal screws seem to be way over priced compared to acme screws.

Lapping with cast polyurethane seems to be working. I ended up using a drill to turn the screw as it was too long to fit in my lathe and it also had a slower speed. I made several passes with some 240 grit sandpaper attached to a wood block before using the lap with 120 grit. It feels quite a bit smoother now. Here's a shot of it after 4 passes back and forth.

http://img.photobucket.com/albums/v649/etfrench/m6_120gritFs.jpg

I'm making a new lapping nut for the 280 grit valve lapping compound which, unfortunately, will take 36 hours to cure

For reference, here's a shot of 1/4-20 plated all-thread:
http://img.photobucket.com/albums/v649/etfrench/Quarter20fs.jpg

The camera is an Olympus e330 with about 150,000 shutter activations. Just about any current DSLR should be capable of taking these images. Of course having a macro spherical panorama head will help :) Here's a shot of the setup:

http://img.photobucket.com/albums/v649/etfrench/Macro%20Pano%20Head/AutoFS_02.jpg

Jaakko Fagerlund
11-02-2012, 05:01 AM
Faster than waiting for the PU to cure would be to just use one or more brass nuts and lapping compound. Even better would be two nuts with a spring between them.

Mcgyver
11-02-2012, 07:07 AM
think of all the great oil retention properties it will have :)

elf
11-04-2012, 10:47 PM
think of all the great oil retention properties it will have :)

I'm not sure what oil retention properties have to do with lapping?

Here's the result after 15 passes with the 280 grit compound and a few passes with different grits of non-woven abrasive pads:
http://img.photobucket.com/albums/v649/etfrench/280gritAndPolishS.jpg

I think it's time to try forming the Acetel nut.

wierdscience
11-04-2012, 11:14 PM
Well that looks better,a few more passes and you'll have 5mm all thread:D

elf
11-04-2012, 11:20 PM
Well that looks better,a few more passes and you'll have 5mm all thread:D

Fortunately, the size isn't all that important :). So far, I've only removed .03mm from the diameter. I wandered around town looking for any other store that carried stainless metric all thread with no luck. (The guy in Lowes asked "What's all-thread?")

SGW
11-05-2012, 06:00 AM
Why stainless? Not that the cadmium-plated steel stuff is going to be any better in terms of finish.

Mcgyver
11-05-2012, 07:25 AM
I'm not sure what oil retention properties have to do with lapping?


the smiley was supposed to indicate it was tongue in cheek, not a serious position.

elf
12-08-2012, 12:48 AM
I just receive some "precision" 1/4x16 Acme threaded rod (http://www.mcmaster.com/#catalog/118/1107/=khxskn) from McMasters. Here's a 5X shot of it straight from the packaging:
http://img.photobucket.com/albums/v649/etfrench/PMax_2687-2772s.jpg

Is the poorly formed crest normal? Will an Evanut just get torn to shreds running on this?

lakeside53
12-08-2012, 01:43 AM
That sucks. It's probably an artifact of the rolling process, but looks like what happens to me if I goof the backlash when syncing a thread early in the process! I doubt that crest will affect much though - the nut will have clearance to that.

Send the picture to McMaster and ask them what to do. I bet they say "keep it" and ship you another.

Astronowanabe
12-08-2012, 01:46 AM
I think you need to steer away from rolled threads if you a better formed thread crest

Mcgyver
12-08-2012, 09:51 AM
Will an Evanut just get torn to shreds running on this?

i wouldn't think it would matter much; its the flanks that count and with a machined thread the crest don't touch.....so shouldn't matter if plastic in the tough of the nut gets scored

Your photography is very good - can you describe the setup/equipment? - I know you put that pic up but what is a "macro spherical panorama head" and what lense are you using?

Richard King
12-08-2012, 01:21 PM
There is a great lappng compound called Time-Savers and it won't embed. I have been lapping brass and bronze with it for years and have never had any issues using it. Can find the info on this site. http://www.newmantools.com/lapping/time.htm

elf
12-08-2012, 02:52 PM
I think you need to steer away from rolled threads if you a better formed thread crest
McMasters doesn't say on their website that this has rolled threads, but ground threads would be a better starting place.


There is a great lappng compound called Time-Savers and it won't embed. I have been lapping brass and bronze with it for years and have never had any issues using it. Can find the info on this site. http://www.newmantools.com/lapping/time.htm
It looks good but the price is more than the budget for this project :)



i wouldn't think it would matter much; its the flanks that count and with a machined thread the crest don't touch.....so shouldn't matter if plastic in the tough of the nut gets scored
I think one of the benefits of an EvaNut is that it is in contact with much more of the thread. I'm not sure how much a ragged crest will affect how it works.


Your photography is very good - can you describe the setup/equipment? - I know you put that pic up but what is a "macro spherical panorama head" and what lense are you using?
A spherical panorama head constrains the camera/lens to rotate horizontally and vertically around the entrance pupil of the lens. The entrance pupil is located at the apparent position of the iris(aperture) of the lens. It's easy to locate by looking at the front of the lens with a small f-stop set. Rotating around the entrance pupil eliminates parallax error, so multiple frames can be combined into a panorama. The macro part is adding a bellows on the camera arm. Focus stacking is done by taking multiple images and changing the focus point between each by the amount of the depth of field (DOF). At 10X the DOF is around 12 microns. The goal for this project is to make a leadscrew that can reliably make 12 micron steps. Actually the tolerances can be pretty loose (relatively speaking) as the movements just have to be less than 12 microns. From a theoretical viewpoint, it's pretty easy to get movements this small with a stepper motor and microstepping. In practice, it's a bit harder because of stick/slip.

The lens for these shots is a JML 21mm f/3.5 which is pretty hard to find. The price for one new is/was around $300, but I'm not sure if they're available new. Here are a couple of macro panoramas done with this setup.

Witch Hazel: http://photosynth.net/view.aspx?cid=ba59da5a-54fd-4809-9234-a91a8c9234fc
Stonecrop: http://photosynth.net/view.aspx?cid=0a00c1a2-7d92-4de5-9488-7bd6ed5f3203