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Threading 1/8 stainless steel

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Eric Cox30/04/2019 16:04:52
513 forum posts
31 photos

I'm trying to cut a 5BA thread on 1/8" stainless steel rod held in the 3jaw lathe chuck. The die starts to cut then the rod slips in the chuck marking the rod. Would I be better off using a 1/8 c0llet chuck.

Dennis Pataki30/04/2019 16:50:56
8 forum posts

I expect you will have the same results using a collet. At least, that was my experience.

I would recommend you use a Jacobs type chuck. I have one that threads directly onto my spindle, and that's what I use when trying to thread rod or bar stock using a die. It holds much tighter than my 3 jaw, 4 jaw, or collets.

You may need to rig up some way to hold the Jacobs chuck. Perhaps threaded onto a straight shank, held in the 4 Jaw. You may need to drill a clearance hole through the shank if threading the ends of long rod.

Hope this is helpful.

ega30/04/2019 16:55:48
1443 forum posts
118 photos

Are you using a suitable cutting oil or paste?

I would certainly try the collet.

How about screwcutting?

JasonB30/04/2019 17:02:37
17081 forum posts
1839 photos
1 articles

Collet usually works better for me and if it does slip won't mark the work as much. Open up the die for the first cut as much as you can then run it down again to get the required fit. Once the die has started squarely you may want to transfer to the bench vice.

Mark P.30/04/2019 18:06:22
610 forum posts
6 photos

Try opening your die up a smidge for the first pass.

Mark P.

SillyOldDuffer30/04/2019 18:27:32
5138 forum posts
1074 photos

Could your stainless be the horrible work-hardening variety? Some of it is evil. Stainless can be difficult to thread and risks blunting the die making the job impossible. Might be worth testing the metal with a blunt saw to see if it hardens. (I've had some success cutting horrid stainless vigorously after the normal approach failed, but you can't really do that with a die.)


JohnF30/04/2019 19:32:31
919 forum posts
114 photos

You will do better with a a high quality ground thread HSS die IMO.


Eric Cox30/04/2019 22:22:15
513 forum posts
31 photos

I'll try the collet

CHARLES lipscombe30/04/2019 22:30:19
104 forum posts
8 photos

Which raises the question of die material. I have heard it said on the forum that carbon steel dies can be sharper than HSS dies and may be a better choice for some materials e.g. brass or stainless steel. That may be the case but would a CS die wear more rapidly than HSS? In my case this is important because I do repetitive tapping of 5mm * 0.8 mm in 303 stainless when making my motorcycle levers.

Trying to thread stainless of any variety with a die that is not quite sharp is only going to lead to tears on this may be a factor in the OP's posting


Simon Collier01/05/2019 00:55:14
314 forum posts
52 photos

I use 1/8 316 for brake rods and thread by first turning down the diameter. I use a collet, a dedicated die and plenty of Rocol.

Pero01/05/2019 04:56:23
94 forum posts

I have had the same experience when threading 3 mm 316 rod (and 6 mm and 12 mm) and have adopted the practice of putting a taper on the end of the rod, getting the thread ( just ) started in the lathe and then moving on to the bench vice.

Using lots of tapping paste but it doesn't seem to help much with the lathe part.

I have had similar slipping problems with threading in the bench vise when using aluminium soft jaws and have had to resort to the very grippy hard steel jaws. It works but the result is not pretty.

At this point I should mention that I have old injuries to my wrists that limit the amount of pressure I can apply to chuck keys and vise handles at times which probably adds to my problem here.

I also get the feeling that there may be a slippery surface coating on stainless steel rod, possibly a residue of the polishing process, which adds to the problem.

On my next outing I intend to try a clean down with acetone before using an ER collet in the lathe. Further experiments to follow .....



Edited By Pero on 01/05/2019 04:56:53

Boiler Bri01/05/2019 06:48:39
813 forum posts
287 photos

The jaws will only have a very small amount of contact with the bar.

I make aluminium blocks for small work holding, about 25mm long. Bore a hole to size and split the block on one side then hold in the 4 jaw chuck. The Ali has a better grip on the bar.


S.D.L.01/05/2019 08:18:04
185 forum posts
Posted by Eric Cox on 30/04/2019 16:04:52:

I'm trying to cut a 5BA thread on 1/8" stainless steel rod held in the 3jaw lathe chuck. The die starts to cut then the rod slips in the chuck marking the rod. Would I be better off using a 1/8 c0llet chuck.

Better with a collet, Degrease material with Acetone or IPA to improve grip.

How are you holding the die?

You could take a couple of thou off diameter


Eric Cox01/05/2019 10:14:14
513 forum posts
31 photos

The die is mounted in a die holder in the tail stock.

plan of attack is,

clean with acetone

open die fully

use aluminium block

plenty of Rocol


S.D.L.01/05/2019 11:52:24
185 forum posts
Posted by Eric Cox on 01/05/2019 10:14:14:

The die is mounted in a die holder in the tail stock.

plan of attack is,

clean with acetone

open die fully

use aluminium block

plenty of Rocol


Check how central the die is in the tailstock die holder. Some have large clearance bores for the dies to be split open and when used push the die up to .75mm (20thou) off centre which is a lot on basically a 3mm thread.

If this is a problem add 3 tapped holes to die holder at 90 degree intervals so that die can be centered , can then be closed up using two side screws.


Ian S C01/05/2019 12:05:16
7468 forum posts
230 photos

I die cut some 10 32 threads on 3/16" stainless rod for displacer rods for hot air motors, I found that I had to cut to size first go as the stainless rod work hardened. The first thread cut I took in stages, and after the second cut that was that, I did get there eventually but the die was shot (good HSS dies used).

Ian S C

Nigel McBurney 101/05/2019 12:59:56
641 forum posts
3 photos

Use a ER collet in a hexagon collet block (from arc euro trade) those collets will grip anything,dont try try using precision lathe collets ,usually morse taper,trying to grip too tightly can spoil them. larger ER collets will even hold 1 1/8 Whit taps without slipping ,and they are superb for making double ended Whitworth studs,no more problems with slippage. Best tooling I have bought in recent years as I do a lot of restoration work, I use ER 32 and 40 sizes

David Jupp01/05/2019 15:44:05
713 forum posts
17 photos

1/8" (3.175mm) is at the maximum of major diameter for a 5BA male thread, according to BS93. That is before any oversize tolerance of the rod, or any extrusion of metal when cutting the thread (which is quite likely with tough materials).

I can see why Simon mentioned turning down the diameter as a first step.

Lambton01/05/2019 16:38:14
692 forum posts
2 photos


You have received lots of good advice about gripping the job and die adjustment .

May I recommend that you try Ambersil "Tufcut" lubricant .that is specifically formulated for turning, drilling, reaming thread cutting and tapping tough materials such as titanium, stainless steel, high tensile steel and high carbon steels. I have used it for years with every success. It is available from Cromwell Tools or most other good tool suppliers.

II have no connection with Ambersil other than as a very satisfied user of Tufcut.


Tim Stevens01/05/2019 18:00:15
1123 forum posts

It might be that the rod is hard-drawn, so the surface has been work-hardened in manufacture. If your job does not need the top end of the high-tensile capability, try the effect of softening the rod with heat.

Cheers, Tim

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