Knurling Straight Wheel?

[Texasbowhunter]

I'm going to be ordering a Straight Knurling cutter very soon and wanted to get some opinions before I order either the wheels or to attachment holder and single wheel...
I presently have a knurling holder where it holds 2 wheels and knurls from the side rather then from the top and bottom...scissors style
Its what I have without buying a pricy scissor style knurling tool...Anyway I digress...
I wish to knurl a project in 3.5" aluminum with the straight knurl and was curious about whether I require a 2 wheeled knurling tool or a single (1) wheel knurling tool
If I use the 2 wheeled then I can purchase the wheels and swap out to fit my present attachment holder...
I had seen where there was single wheeled straight bar style attachments for sale as well
Which is preferred?
The single wheel or the 2 wheel?
Thanks
Paul

[Rich Carlstedt]

For "Straight " Line Knurling you only need one wheel
Cross-hatch Knurling requires two wheels to create the cross-hatch - they can be mounted on a linear feed holder, or a scissors holder
Scissors knurling tools provide a method that eliminates/reduces force on the cross-slide
Single or dual linear wheels load the cross-slide quite a bit.

Rich

[BCRider]

The single I use works well. Especially with aluminium. In fact I need to be a little careful on aluminium or I overdo it and the finish becomes dull.

12x36 lathe is OK with the pressure needed. Single wheel doesnt need as much as a two wheel former.

[Texasbowhunter]

Thanks Guys
Paul

[Bob Engelhardt]

...
Its what I have without buying a pricy scissor style knurling tool
...

Everybody has their own idea of pricey, but at $30, I think that this one is reasonable:

https://www.amazon.com/gp/product/B07D3TQJHG/

But, it would need 2 wheels.

[Toolguy]

That one goes to about 1 inch (25mm). Paul needs one that will do 3.5 inches.

[Texasbowhunter]

The single I use works well. Especially with aluminium. In fact I need to be a little careful on aluminium or I overdo it and the finish becomes dull.

12x36 lathe is OK with the pressure needed. Single wheel doesnt need as much as a two wheel former.

As most or all of you may have gathered I'm just getting started with this craft...
I was not aware of this minor detail as far as to much wasn't good for the finnish...Thanks for the tip
Paul

[Bented]

One or two wheel knurling tools that plunge into the work from the side are commonly called bump knurl tools, as mentioned these produce a good deal of load on the part.
A scissor tool lowers this load a great deal, most of the force is constrained to the tool, I have fractured HSS knurls in the past by being to aggressive (-:


However they were very course knurls with a fixed finished diameter as stipulated by the customer.
This is the test part that fractured the tools, the always lovely stainless steel.

[Paul Alciatore]

Wish you hadn't told me that. Now I will surely break one on my next knurling job.

One or two wheel knurling tools that plunge into the work from the side are commonly called bump knurl tools, as mentioned these produce a good deal of load on the part.
A scissor tool lowers this load a great deal, most of the force is constrained to the tool, I have fractured HSS knurls in the past by being to aggressive (-:


However they were very course knurls with a fixed finished diameter as stipulated by the customer.
This is the test part that fractured the tools, the always lovely stainless steel.

[Rich Carlstedt]

General Comment on Knurling ---or just observations you might say.
Many machinists look at knurling as a similar " Oh No ! " issue as "Parting Off" is

Step back and look at what you are doing.... and it is really easy to see with straight knurls so I will use it for my explination.
You Know what gear cutting is I presume.. a 12 Pitch gear cutter will cut 12 teeth on a 1" Pitch circle (PD !) , but the overall diameter of the gear will be slightly larger, say 1-1/8" in order to do so correctly. SO it is with Knurling tools !
Look at bented's photo and I thinks it shows "16" as the "pitch" of the cutter. This tells you the pitch that the cutter was designed for .
Now the difference between a Gear Cutter and a Knurler , is the Gear cutter " Removes" stock and the Knurler "Moves" stock --but pay attention to the Pitch !
If you try to use a gear cutter to make more teeth on the same size blank , ( say 18 instead of 17) you wind up with shallow teeth and they are NOT formed correctly or look right !
The same applies to knurling
For simplicity sake, lets say the pitch "Circle" on the knurling tool is .100" apart .
That means if the pitch circle on your part is not divisible by .100 you will have a more difficult time. Instead of the tool impinging into the work to make the perfect knurl crests
it will slide from one to the other ( Must lube !) and form wider valleys to achieve the desired crests, or when the pitch / diameter mismatch is really bad The Knurling tooth encounters a previously formed "Crest" and crushes it and you get a garbage knurl as the Knurl Pitch cannot match the part diameter. ... This is a major reason to start at the edge and get the knurl correct , and then proceed with side feed . Ever notice all those "flakes" on the oil ? Its caused by sliding and not impinging.. And know that sometimes the reason for you failure is your part diameter needs to be changed slightly to match your tool.

So how do I get a perfect knurl - you ask
For general work you can try and see if your work diameter works with the tool you select, but for critical work where you want the perfect knurl, I suggest you try several different diameters
and measure your cross-slide feed so you know how much to load. It only takes a few thousandths on diameter to make a world of difference in results

Hope this helps
Rich

[sarge41]

I'm glad to see the explanation that Rich has provided for the correct procedure for knurling. At first you may scratch your head and ask what is he talking about. After you have read it several times, and thought about it, you will start to understand it. Many on this forum will tell you that working with the pitch of your knurling tool is not important, but it is. Thanks, Rich.
Sarge41

[BCRider]

To add to Rich's post I have found that it is harder to get a clean start with the single wheel "push" coining or straight knurl than it is with the diamond knurls. Likely something related to that ability to "slide" or slip. A diagonal wheel can slide easily. A staight coining wheel cannot slide at all.

I'll have to set up some alloy scrap and play a bit more with sizes and finishes.

For sure though pressing in on aluminium with much more than what is needed to JUST get crisp looking crests is a recipe for lots of flakes in the oil and a dull grey finish.

[DR]

I understand the point Rich is making. But.....

I use a couple varieties of knurling tools all with opposed wheels. I never worry about blank diameter and the knurls created have all been satisfactory to my customers. Actually sometimes I'll turn the blank smaller or larger rather than adjust the knurls because it's easier than adjusting knurl spacing.

Bented mentioned his customer specified a finished knurl diameter. I had a couple of those over the years. Instead of trying to get the correct finished knurl diameter we just took a light skim pass over the knurled area to bring it to size. To get a knurl to come to a certain diameter can be a nightmare since any small variation in blank size has a larger effect on diameter of knurl.

[Bented]

I suspect that the customers engineers had a good laugh, they gave me a finished knurled diameter that may be dusted off .005" after knurling, a knurl pitch of 12 and no start diameter, the parts have an 8"+ long surface, it took a few trial and error tests to get the starting diameter correct. These are recurring parts, the stock for every order comes from a different heat making consistency nearly impossible.

I also make similar parts in aluminum, they are rarely consistent from bar to bar.

[Bented]

Wish you hadn't told me that. Now I will surely break one on my next knurling job.

Don't worry, Paul you are never likely to have to push a tool that hard, everything is Peaches and Cream until you try to get that last .010" of diameter increase out of it, this is when things break.

Also you are more likely to have traditional non bearing knurling wheels seize on the axle due to speed, do the math.