Best grade of stainless steel for knurling in a hobbyist lathe?

[Mike Davies 3Participant @mikedavies3]

Hi,

Question as title:

I have some small parts ~dia around 8mm that I need to be knurled in my Boxford 5″ and wondered what the best grade of stainless is in respect of knurling ?

Thanks,

Mike

[Brian WoodParticipant @brianwood45127]

Mike,

Much depends on the knurling tooling you have. If you have a ‘push on’ type of knurl then it will be hard work. Stainless steel of most grades readily work hardens and this form of knurling depends on the strength of the lathe to be able to deform the workpiece sufficiently before it is too hard to work.

The other form with opposed knurls works by loosely clamping the workpiece without the need to force it into contact as above. The clamping clearance can be adjusted as the knurl forms.

Use plenty of coolant to wash away chips that will otherwise become embedded, run the job slowly, as low as 30-40 rpm and work the knurl backwards and forwards along the job as it goes to chase the knurl rather than concentrate effort in one area.

Brush the job with a stainless brush when done to soften the raised points a little and remove any loose chips and dust

Try 316 rather than 304 as a first attempt

Regards   Brian

[Mike Davies 3Participant @mikedavies3]

Hi Brian,

Thanks for the tip on 316 vs 304, I wouldn’t have guessed that.  It is a clamp style knurler and I wouldn’t want to use another type on my Boxford, they’re not the most massive machines out there…

So I can experiment with my set up, what is the easiest metal to knurl with out of all the usual suspects ?  I might have a play before I go out and buy some stock…

Thanks again,

Mike

[FulmenParticipant @fulmen]

I would choose 304. I don’t know how well it knurls, but 316 is a true PITA. You might even need a cut knurl for this.

[Howard LewisParticipant @howardlewis46836]

When knurling any material, I try to use the lowest possible speed and axial feed.

FWIW, With the ability of stainless to work harden, I would try to make the knurl, with a clamp type knurling tool, in one pass, about 0.010″ (0.25 mm) deep, with plenty of lubrication.

Howard

[bernard towersParticipant @bernardtowers37738]

I have to admit that knurling stainless is not my most favourite job but for a particular job I do on 16mm dia is to cut it on the shaper as it needs to be quite long. but IMHO if you do knurl it conventially do it in the shortest possible time to prevent work hardening.

[duncan webster 1Participant @duncanwebster1]

No-one has mentioned grade 301,but as it claims to be higher tensile than 304 it’s probably not a good idea

[Brian WoodParticipant @brianwood45127]

Mike,

You asked for advice on the easiest metal to knurl as practice material. Aluminium has to be the one, but it might be too soft to be realistic so I would recommend mild steel

I have knurled steel perfectly satisfactorily on my Myford S7 so I imagine a Boxford would have no trouble being a heavier build. I have not tried knurling stainless steel but I have machined both grades 316 and 304 with carbide tooling. Some say 304 is a pig to machine, not in my experience, it was no worse than steels.

I hope that helps you

Regards   Brian

[jimmy bParticipant @jimmyb]

I’d go with 303. You won’t have any issues, as this is free machining.

 

Jimb

[noel shelleyParticipant @noelshelley55608]

The OP does not say why he wants to use stainless . Is it for it’s stainless properties ? If so and in water or steam then 316 . There is little point in practising on a different metal that will have very different properties, eg brass or ali. Noel.

[jimmy b]

On jimmy b Said:

I’d go with 303. You won’t have any issues, as this is free machining.

 

Jimb

I agree, but ‘free machining’ is relative!   303 is the most machinable stainless, but its only half as machinable as EN1A.  Far better than the difficult stainless alloys, but still a bit nasty.

Most Model Engineers knurl by squeezing with a roller, or – much better – squeezing between rollers.  Far from ideal when the metal being squeezed is likely to work-harden!   Knurls on manufactured products dodge that problem by being cut.  Doesn’t help, because the tooling they use is expensive.

I avoid machining stainless steel unless there’s a specific reason for using the stuff.   Some stainless steels come straight from hell!

Dave

[jimmy bParticipant @jimmyb]

I have machined 303, 304 and 316 at home for 20 years (for a profitable side line). As has been said, horses for courses.

 

303 is “easier” to machine and should take a knurl fairly well.

Work hardening can be an over used term, blunt or inappropriate tooling can (in my experience) be more likely.

 

I’ve spent over 40 years machining 300 and 400 series stainless, as well as all manner of “exotic” materials.

 

Jimb

[Mike Davies 3Participant @mikedavies3]

@Noel: Thanks for your reply, I need the material to be stainless because it is going into wood and rust caused by moisture in the wood would be unsightly (it’s a bush in the headstock of a guitar). Stainless will also have a similar appearance to the plated components in the guitar so it will look ok too.

My thoughts on a practice piece was to set up the diameter and “depth of form” on a material which won’t work-harden to the same extent as stainless.

Thanks to all for the replies,

Mike

[JasonBModerator @jasonb]

Is the knurl going to be visible or are you using it to grip in the wood or to help with an adhesive bond?

If it is not seen then a series of shallow Vee grooves would do the job, make them asymmetric like a hose tail and they will push in easier than they pull out.

[Mike Davies 3]

On Mike Davies 3 Said:

… it’s a bush in the headstock of a guitar. …

That’s good because hidden knurls need not be beautiful.   Knurls often have a major aesthetic role, and it’s important these be clean.

My thoughts on a practice piece was to set up the diameter and “depth of form” on a material which won’t work-harden to the same extent as stainless.

Always good to practice, but don’t be surprised if the material used changes the result!

One way of visualising how a knurl works is that the ridges on the knurl first dent the work, and then, on the next rotation, the ridges engage with the dents.  In this view, a regular pattern emerges because the ridges engage with the work like teeth on a gear.

I’m not convinced the ‘like teeth on a gear’ model is true, or maybe it’s only part of the story.   One problem is that the ridges on a knurl are on a fixed diameter.   Gear cutting requires an integer relationship between the diameter of the gear and the cutter, whilst knurls work well enough across a much wider range of job diameters, even if the integer relationship isn’t met.

I suspect knurls work by squeezing the material, not by cutting.  If knurls are squeezed rather than cut, the mechanism is more like a tyre leaving a plastic impression of its tread in mud.

As Aluminium, Brass, Mild-steel and Stainless all have different plastic properties – how soft and springy they are – don’t be surprised if practice knurls are not the same as real ones.   I think the movement allowed by plastic squeezing also explains why knurling is a bit hit and miss.

If plastic squeezing is how knurling works, then work-hardening stainless is much more likely to cause trouble than other metals.

Manufacturers make consistently gorgeous knurls by cutting them with a special tool, not by rolling.   Unfortunately knowing that precision knurling is available doesn’t help the small workshop much because knurl cutters are off the scale expensive!

 

 

Mike

Dave

[SillyOldDuffer]

On SillyOldDuffer Said

I suspect knurls work by squeezing the material, not by cutting.

You can do it either way, but the tools most of us has is indeed cold forming the knurl. This works fine on most materials but some work harden too much for it to be practical. Making a cut knurl tool isn’t that hard and the wheels are affordable, there are several build videos on youtube.

Annealing the stock might also be an option.

[CirclipParticipant @circlip]

Don’t know how any times I’ve posted this, an effective search facility might help, Whatever grade you use, go for the ‘L’ composition. I.E. 304L or 316L. The L denotes Low Carbon, so easier to machine. If you’re pressing fixings into the wood there are numerous Brass or Alumininininium threaded inserts to help.

Regards  Ian

[Circlip]

On Circlip Said:

Whatever grade you use, go for the ‘L’ composition. I.E. 304L or 316L. The L denotes Low Carbon, so easier to machine.

Sorry, not quite correct.  The L does denote low carbon – this is to avoid problems with weld decay (where Chromium Carbides form in the heat affected zone near the weld).   As the 300 series stainless steels are austenitic, carbon level won’t materially affect machinability.

[CirclipParticipant @circlip]

Made the MEW rotary table for rounding the ends of link rods etc. years ago, ALL Stainless (cos I had access to it). Knurdling of 8mm dia. operating lever/handle an absolute b8tch using 304, a dream using 304L with a push on double roller knurdling tool, NOT a clamp type, Emco V10 lathe.

Regards  Ian.

[Nick HughesParticipant @nickhughes97026]

At work, for one off or very small batches of components in tougher materials such as EN24T, various grades of Stainless Steel, Titanium etc, we use a Clamp type of Knurling tool, fitted with Convex Knurl wheels.

Although significantly more expensive than the more usual flat faced knurls, the Convex knurls have always produced a good sharp Knurl (had many failures with standard knurls)

For larger production batch runs on the CNC lathes, we exclusively use Cut Knurling.

[Mick BaileyParticipant @mickbailey28509]

For press-in guitar bushes in stainless you can plane them with a lathe tool set sideways. I turn a shallow runout groove and use a simple index using a change wheel. I’ve made bridge, tail piece and tuner bushes using this method. It’s slower than a rotary knurl but reliable.

[Author]

Posts