Knurling ?

[Ken_Shea]

When knurling how can you assure that you will get an even pattern around the circumference with out cross knurling over the previous cut.

Thanks
Ken

[HuFlungDung]

Hi Ken,

For a normal cold forming knurl, what I have found works pretty well, is to start with just about 1/4 of the width of the knurl engaged on the part. Feed in quite suddenly to full depth, because the pitch changes according to the depth, so you might as well get it over with right at the start.

Another trick I use is to angle the knurls a couple of degrees from perpendicular to the surface. This make the leading edge of the wheels "dig in" for a more positive bite.

It is difficult to know what full depth is, but on a manual lathe, I just go by feel. Then, back off a bit and begin the traverse feed, and the wheels will continue to track well in the heavy pressure area where you began.

I usually knurl to full depth in one pass.

Cutting knurls are different because you start clear of the end and feed in. I believe that the pitch diameter can be calculated and the depth set according to the pitch of the knurl.

[Gunner]

Ken,
Are you knurling in production or just for looks? The standard variables are the number of teeth required on the circumference, the blank diameter, and the number of teeth per inch required on the roll. Hu flung dung is correct with feeding in hard. When knurling you are displacing material. The material from the root of the the knurl is flowed to the crest. Once you get the material moving, you want to keep it going. I have some information, tables, and formula's if you need them.

Gunner

[HuFlungDung]

Somebody makes convex knurling rolls which I think would be great for situations where you don't have to knurl up to a shoulder. Probably by Dorian? Its what I would buy if I had some serious amount of production to do.

They make an opposed roll tool which takes the pressure side-load off of your workpiece and machine and concentrates it within the holder itself. Just costs $$

[Ken_Shea]

Gunner, this is for personal and not production. Could be I am not starting hard enough for the knurling cutter to stay in the previous cut. I will try that.

I take it the knurling cutter circumference does not have any particular circumference relationship requirements with the blank stock then?


Thanks for the input Hu and Gunner.

Ken

[HuFlungDung]

Well Ken, theoretically, it does have a relationship: the pitch circle diameter of the part should be a multiple of the pitch of the knurl. However, in actual usage, there is so much flex in everything, that it is a practical impossibility to determine if the tool is beginning at the pitch circle depth, and staying there as it engages the work.

[Gunner]

Ken,
Here is a website with knurling information. I just looked at it quickly but it looked like it contained similar information to the manual I have. It may explain it better than I can.

www.doriantool.com/textdex.html

Gunner

[Ken_Shea]

Thanks Gunner, I will take a look.

[9566317]

Get the knurls in fast and feed fast .020 is
standard.If you want pretty use straddle knurl holder to eliminate the fllex in your part and again get in and go.On a screw machine we always feed on at about .015 to .022 and of at .025 to .040.This is done from the turret though.I have done it on an engine lathe though.Get ahold of Form Roll and they will give you the books and the
formulas for knurling.I have even knurled splines.Not fun though but posiable

[ballendo]

Ken,

Entire books have been written on knurling and selecting the proper starting diameter...

But that mostly relates to ending up with a pre-defined overall diameter, important when knurling is used in press fits...

For "pretty knurls", you only need to realise one thing. The pitch diameter IS going to be some multiple of the knurl spacing. Here's what happens:

You start your cut on some arbitrarily sized diameter, and as the cut comes around to the start, the "new" marks don't match the old marks because the circumference--at that diameter-- is NOT evenly divided by the knurl distance. Which is okay, since you're wanting full triangles, not "lines" anyway!

As you feed deeper, you will reach one of two points first: Either the bottom half or the top half of the knurl "fills". Unless you are lucky and the arbitrary diameter you've started with causes the perfect knurl! Think about what is happening...

As you increase the cut, you are "flowing" the metal in the valleys to make the "hills". Ideally, when the valley is cut full depth, the hill ALSO reaches its peak--fine points at the top. But this will only happen when the diameter halfway between is a multiple of the knurl spacing. (This is a simplification; like I said entire books have been written about this)

If the diameter is larger(than the ideal), the valleys complete before the hilltops are fully formed. If you continue to cut deeper, You'll see "double" valleys, with sharp hilltop points. Sometimes this result is considered a decent knurl. Because we notice the points more than the valleys...

If the starting diameter is too small, the hilltops form before the valleys are fully cut, and you start to "skid"-- like the overlapping lines at the beginning of this explanation. This means the hilltops are crushed by the continuing cut, so as you cut deeper you have double hilltops with sharp single valleys.

What's kinda nice is that you can often "hamhand" it and get by pretty well. But if you really want good, crisp knurls do a bit of experimentation to get a good starting diameter, using what I've written above. Once you have the starting diameter for a given knurl and material, you will have it forever... (just use sharp knurls)

Hope this helps,

Ballendo

Originally posted by Ken_Shea Gunner, this is for personal and not production. Could be I am not starting hard enough for the knurling cutter to stay in the previous cut. I will try that. I take it the knurling cutter circumference does not have any particular circumference relationship requirements with the blank stock then? Thanks for the input Hu and Gunner. Ken

[Ken_Shea]

Thanks again for all the input, it has been a big assist in understand knurling. Like so many aspects of machining there seems to be some hard and fast rules that apply some of the time especially when all the variables are in your control and can be just a matter of feel when they are not. Kind of a flying by the seat of your pants sort of thing that comes from experience.

Ken

[marto74]

Hi,
We do big quntities of turned brass parts with knurling by DIN 82 0.5 and 0.6 mm pitch ( the parts are 6 - 16 mm DIA)
The CNC automatic lathe is working 24 hours and usualy we need 1-2 hours to set the knurling then the machinetools make 10000 - 15000 pcs with perfect knurling.
We had some problems with the shape of the knurling in the past .
Now we are workin with knurling wheels ZEUS from Hommel+Keller
http://www.hommel-keller.de/
The best result of one knurling wheel is 150 000 pcs - this was 0.5 mm pitch GV 30 .

Regads: MArtin