Getting a handle on knurling, thanks to Keith

[Pistolero]

In my learning to do machine work, Keith provided a really key piece of
one part of the puzzle, knurling.

I had succeeded on knurling one workpiece and then the next, similar piece was
not particularly nice - yes, rough, non-slip, but looked wrecked and ugly, unlike the
nice, crisp knurls we see all the time on reloading dies.

So, using Keith's information, and example spreadsheet, I worked out my own
spreadsheet, since my wheel sizes and number of teeth per wheel were different.

I just tried three different diameters which the spreadsheet said should be modular
and produce good knurles. The key is basically you need the pitch of the teeth to work
out evenly, sort of like cutting gear teeth around the circumference of the work. If the
diameter is right, the wheel keeps matching the first pass, and the teeth get deeper.

Here is a sample piece which I tried three different diameters which should work with my
knurling wheels.



I am pleased with the results and would really like to thank Keith for the education.

Bill

 

[Brad]

I can attest for the fact that some diameters knurl well with my tool and some just suck. I never took the time to calculate the numbers but I'm sure this is why.
I suppose I need to see what the wheels on mine measure and do some math.

 

[Pistolero]

Brad,
Get me your wheel OD and # of teeth and I can send you a spreadsheet very quickly.

I am going to print out a sheet for my knurler and have it laminted to keep by the lathe.

Bill

 

[fiver]

isn't it similar to cutting checkering?
you'd make a pass on the roll and then move over and do it again then cut deeper then go the other direction to make the diamond points.
or at least that makes sense to me.

 

[Pistolero]

No, not done like checkering, even though the result is pretty much the same appearance.

A better analogy is cutting gear teeth. A knurling tool has a fixed diameter rolling wheel (pair) being
pushed very hard into the material (two wheels in opposition with my tool). The trick is to get the
diameter right so that the circumferential distance is some even number of teeth so the wheel
rolls in the same grooves on successive passes as the lathe rotates. The screwed/bad up knurling comes
from an in between diameter, the knurl is just churning up the surface, hitting different spots
on successive revolutions.

So, you select one of the 'modular' diameters which will give you a good fit. For example, my 46 tooth
0.800 diameter wheels have a pitch of .055". So, if you have any work piece circumference which is evenly
divisible by 0.055" with NO REMAINDER, it will work. Say you start with 25 teeth. 25 x .055 = 1.375 inches, but
this is the circumference. So, divide by Pi (3.14159) to get the diameter, which is 0.438" diameter, which
happens to be the size of the middle knurl in the photo. A 26 tooth knurl would also work, and it would
require a 0.455" diameter. You can select any number of teeth around the knurl, but you have to select
the correct diameter to get it to work properly.

Keith explained it a while back and the good/bad knurl mystery disappeared. I also have wheels with 30 and 68 teeth,
same diameter, for finer or coarser knurling. This 45 tooth knurl seems good for me now. I may try the other ones out,
just make some samples to see how I like them and what they may be good for. The pitch of the coarse one is 0.084",
and the fine one is 0.037" If I was working with approximately 0.438 diameter part, and wanted to make a
fine knurl with my tool, I would use 0.436 diameter and get 37 teeth, or for the coarse knurl, I would use 0.427
diameter, or 0.454 diameter for 16 or 17 teeth. Size matters.


Bill

 

[JSH]

Bill, sounds like your having a good time.
I saw Warren Sunday at an IHMSA match. We had a good visit. We got to talking about 200 meter accuracy with the wheel guns. I need to get back with him again. I may get a hollow point mold to try out his thoughts.
I almost gave a holler to see if you were in the shop Sunday. Went by on 10hwy, looked at the clock and didn't. I was on a mission for new work boots. I was once again disappointed in Vanderbilts selection of Red Wings, let alone boots period.
They had some pretty stylish safety toe boots, but nothing that I deemed usable. One style of American made Red Wings, I tried them the last time. They fall on the cheap end, I had all the stitching burned out from cutting and welding in a couple of months.
I worked at Vanderbilts in Leavenworth back in the 80's. We had at least one example of every current Red Wing style.
I got ticked and just went to the Red Wing store. Paid a few bucks more, but service sells for me! Nice young lady helped me out, very knowledgable on the product. She put me on to a pair and then showed me some on clearance,lol she is a good sales person. I went for one pair and ended up with two!
Jeff

 

[KeithB]

Bill, glad things are working out for you. Those are very nice knurls. I knew that if you thought about it in terms of something an engineer such as yourself is familiar with, i.e. spur gear teeth, that it would be very easy for you to carry it to it's logical conclusion. You certainly gave a very clear explanation of the principle of the thing, good job on that. Good idea on laminating the printed spreadsheet to hang in the shop. I did the same thing for a reasonable range of diameters for my three knurling wheel pitches and put the documents into clear plastic pockets in a three ring binder that we keep in the shop.

 

[fiver]

okay.
now I see what your saying.

just so I am clear.
[simple English] the angle of the cut changes with the diameter of the piece.

I was gonna ask how you got pieces the correct diameter for the math to work out,
but then recalled you got a lathe sitting right there somewhere in the vicinity..[duh]...slap me,, it's early.

 

[Brad]

Ok fiver. The part to be knurled has a specific diameter. The knurl, which does the work, has the working edges a specific space apart. We want the knurl to roll around the part so the working edges always land in the same spot as the part rotates against them.
We control how closely this happens by controlling the diameter of the part. If the part is right on then those working edges always land in the same place all the way around. If the part is t the right diameter the working edges end up 1/3 or 1/2 line off on each rotation. This means that instead of making the knurl deeper each time around it is trying to continuously cut a new knurl on each rotation. This leads to a knarly knurl.
We can make the part maybe .015 larger or smaller and suddenly get a perfect knurl instead of a mess. It really can be that small of a change that matters.
I need to measure the picth of my knurl. I plan to coat it with some moly grease, lightly, and run it along a sheet of paper. By counting say 50 lines and measuring the distance between the lines I will know the pitch. I can then let Bill do his spreadsheet magic.

 

[Pistolero]

Keith,
Thanks for the explanation. It is amazing that I had not really grasped what was going on until
you explained it like gear teeth, then it just made perfect sense why I was messing up the knurls.
I have always appreciated a skilled machinist, and as I learn more about it, I see that there are SO
many tricks to this trade.

Hmm, fiver -

Yeah, the quich change tool post is great. Put in a cutter, turn the diam you need, then swap in the
knurling tool, and center it up.
HMMM - I have to think on that comment on angles. OK, depending on what you mean by "the angle of the cut".

The angle of the diamonds stays the same as far as the overall pattern, set by the wheel cut. If you are
looking at the angle between two radius lines drawn through the peaks of adjacent diamonds, yes, that will change
as the work diameter changes. The pitch is the same, so if you have a 3" diameter workpiece, 0.055" is a
small angle. For a 0.25" workpiece, the same pitch, 0.055", is a larger subtended angle between each
peak....better way to say it is how many teeth around the part. On a 3" workpiece, circumference
is 9.425", so there will be 171 teeth (approx, 3" is not an exact knurl diam). So each tooth subtends
360/171 or about 2.1 degrees. For the 0.25" diam workpiece, the circumference is 0.785, divided by 0.055"
gives you 14.28 teeth (so 0.25 is not a correct knurling diam, but OK for angle comparison) and for
14 teeth, each tooth subtends 360/14 or 25 degrees. So, you are right, and I hadn't thought of it in
that way.

Jeff,
I hope you have the Sheldon installed and running. If you have any issues, don't hesitate to call.
I still have a soft spot for that machine, it is a good one and it taught me a lot.
Haven't talked to Warren in a few weeks, at least. I'd take his advice on long range accuracy, at least
on the gun end, and whatever loading recommendations he can give, too.

I got my new Redwings (now several years old, but still my new ones ) at the Redwing store
on 95th near Antioch. Yes, the young saleslady was very helpful, I was surprised that a pretty
young lady would be working that job, but she seemed to know her stuff. Don't care who you are
as a salesperson, always appreciate knowledge. Used to be you never saw women in "men's jobs",
and I never begrudge them a bit of it, as long as they know their business. The first real surprise
like this came when I was about 18, rebuilding a friend's Ford 8N tractor. Went to the rural Fla Ford
tractor dealer and the parts lady set me up with a complete rebuild kit for an amazingly low price. She
really knew her stuff, too, as we talked about which parts needed replacing,and which would go again
plus a few tips like thebest way to get the old dry liners out.
I always appreciate knowledgeable sales help.

Bill

 

[Pistolero]

Smart way to measure, Brad. I cleaned the wheels, got out a fine sharpy and a bright light,
and my close up reading glasses and marked every 10 teeth. Counted twice, too.

Bill

 

[Brad]

Lots of neat tricks online Bill. The hobby machinist forum is one I look at daily. Pretty sure Jeff does too.
Seems logical to me to get advice from others who have similar equipment and needs.

 

[Pistolero]

What specific forum? Just Hobby Machinist?

 

[smokeywolf]

One more little tidbit to knurling; particularly with sticky stuff like aluminum. If at all possible, use either flood coolant or a mister (spray mister). Aluminum and other soft, sticky materials tend to shed particles as you knurl that cling to the knurling wheels and to the crevices in the knurl on the workpiece. The flood coolant or mister continuously wash those particles away, resulting in a much cleaner looking knurl.

 

[Pistolero]

Thanks, smokeywolf. Those were done dry and even after a quick wirebrushing with a
hand brush, there are bits of aluminum left. I will try some sort of a hand pumped
lube spray or maybe a normal pressurized can of WD40 to rinse it as I knurl.

 

[KeithB]

Good point smokeywolf; since I normally flood cool w/soluble oil I never really noticed it, but I do recall in long times past dry knurling some aluminum on the manual lathe and getting some particle adhesion.

 

[Brad]

What specific forum? Just Hobby Machinist?

http://www.hobby-machinist.com/

 

[JSH]

http://www.hobby-machinist.com

Get a comfy seat and your reading glasses.
A wealth of information.
The bad thing is all of the neat projects!!!
I do a search over there, one thing leads to another. The next thing I know I am some place, don't know how I got there, AND, forgot what it was I was looking for!
OH LOOK, a squirrel........
Jeff

 

[Brad]

Yes, it's of neat projects and ideas. I have learned a ton there.
I keep noticing posts by this JSH guy.....

 

[Pistolero]

Went over a few yours back.... wandered off on color case hardening, spent a couple hours...
Interesting but I'll likely never do any color case hardening. Or maybe now, I might.

Bill