First ever attempt at knurling...

[darkzero]

If you don't get flaking then you are doing good.

I knurl in one pass only, mainly to prevent work hardening in titanium but flaking as well. Luckily my lathe & knurling tool can handle it. Some machines can't so if you have a less rigid machine, you have to knurl with multiple passes. Especially with a bump knurler, I hate those things.

Soft materials like aluminum flakes very easy when knurling a full form & multiple passes, you will not see the flakes falling out of the wheels, they get stuck in the teeth & when rolled over they will embed into the workpiece. If you flood with lubricant you will see the flakes flushing out of the wheels. It's very fine, not like a chip.

Most knurling wheels that I'm aware of are HSS or cobalt. I use pvd coated cobalt wheels. I doubt they make knurling wheels in carbide but I have no idea.

Just to be clear, I'm talking about form knurling. Cut knurlers do produce chips.

 

[Tozguy]

DK, my comment about different wheels for different materials refers to the pitch of the teeth in the wheel. Seems to me that finer pitches would work better for harder materials and vice-versa. Do you use the same pitch knurling wheels for aluminum as for titanium?

Do you consider that flakes from knurling aluminum are unavoidable?

 

[Tozguy]

This is a good read on knurling.
http://www.genswiss.com/knurlingtips.pdf

 

[darkzero]

I don't base the pitch of the wheels according to the material being knurled. Never thought of it that way. I base the pitch of the wheels on the material diameter & how fine of a thread I want, cosmetically. So yes, I have used the same pitch wheels on all the different materials I knurl. With smaller diameters I use finer pitches.

I would say flaking can be avoidable depending on the type of knurl being formed, like for partial form knurling or short bands. Convex wheels helps a lot when axial feeding. I really like the convex wheels & is pretty much all I use unless I'm just knurling a single band.

 

[Tozguy]

Thanks for the reply.
The two knurl forming tools that I have came with 16 tpi knurls. They work great on aluminum but not on harder material. There seems to be a limit on how far I can force the knurls into some steels. It takes more passes than for softer metals and just seems to fuzz up the surface. Logically a finer knurl should work better (fewer passes) on harder metal. Knurls are available in increments to as fine as 80 tpi if not more. Convex knurls make sense and are now on my shopping list.

 

[TTD]

Well OK then, guess my inexperience was showing through & I was just being too paranoid/critical of my work…thank you much for the comments & much needed boost of confidence, guys!

This place is absolutely awesome…the wealth of knowledge found here is incredibly mind-boggling, only to be surpassed by the friendly, courteous members who take the time to steer us newbies in the right direction…I tip my hat to all of you!

 

[mikey]

In my experience, all materials flake when we form knurl them. We are basically work hardening the surface as we knurl and this hardened surface is being moved around. As this occurs, planes form between the hard surface and the softer unhardened surface and separation occurs, causing flakes. The more passes we make, the more this separation occurs and the more flakes we see. It just is.

Lubrication makes a difference, at least to me. I prefer using sulfur-based extreme pressure lubricants when knurling. Like screw cutting, knurling is a high pressure situation and the EP additives make a difference in the pattern. It lubes the pins well and I also get less flaking.

I've been thinking about knurling tools ever since Will started working on my mind and I've come to the conclusion that a hardened knurling tool with appropriately massive arms with minimal play at the arm joints and tight fitting hardened (carbide) pins will make for a better tool. My current favorite tool is shop-made and it is excellent but it would be excellenter if it was hardened, which it is not. An Eagle Rock knurler is in my future and thanks to Will, I know which one to buy.

 

[Dr John]

Needed to knurl a piece of 6061 aluminum that measured .819” o/d (according to my knurling chart) x 1” long x 21P (medium) for a cocking bolt knob on an airgun project I’m doing. Never knurled a day in my life before, so I was a bit apprehensive on how I was surely about to mess this up. Have watched tons of videos & read lots of articles on the subject, but no hands-on experience…

Now, a smart fellow would chuck up a piece of scrap, turn it down to the correct diameter & make a few practice runs so he would have some clue what to expect, but not me….may as well learn on the fly!

As it turned out, I didn’t have any more 1” round bar left so was forced to turn down a piece of 1” hex to 0.819” o/d x 2” long. Then set up the scissor type knurler so only about ½ of the cutting wheels were actually touching stock at TDC & BDC. Tightened up scissor “snug-but-not-to-tight” & turned chuck by hand to see how badly out of sync the wheels were. To my amazement, they “seemed” to look ok so tightened it some more, had a smoke to calm my nerves & went at it. Ended up making 3 passes (tightening more each time) with lots of A-9 cutting fluid used. Speed was around 50-60 rpm & fed in with hand crank.

Overall, I guess I’m fairly happy with how it turned out to say it was my first time knurling, but still doesn’t look near as clean cut as the many photos I’ve seen here on the forum….there are some sweet looking ones!

(see pics below)
Maybe my wheels are not sharp or hard enough?
Too deep a cut? Not deep enough?
Quit buying Chinese crap? (guess that’s a no-brainer, huh?)
Any ideas on what I should be doing/looking for to fix this???

Just guessing here, and I know inexperience is playing a major role too, but I also think part of my problem could be the cheap (but all I can afford) Chinese equipment I’m using:

Craftex 7x12 mini lathe: http://www.busybeetools.com/products/lathe-mini-7in-x12in-1-2hp-cx-series-csa-cx704.html

Knurling tool: http://www.busybeetools.com/products/knurling-tool-for-mini-lathe.html

Pass #2 of 3

And no, the points on top aren't mashed beyond repair... crappy light casting a weird shadow on work...points really are all there!

Looks very good, to me. I usually try to knurl in a single pass, avoiding any misalignment. I gradually tighten the knurls while stationary, to find the shape I want and then start moving. I have used a variety of knurls and quality doesn't seem to be an issue on most metals.

 

[TTD]

Thanks, DJ...I appreciate the advice!

I will definitely try your single-pass method next time around, but not sure if my 1/2hp, 7x12 has the ponies to make a single-pass knurl....I managed to stall the poor wee thing on the second pass .

In the wee girl's defense though, I was only spinning at around 40-50 rpm....suppose I could grow a set of berries myself & speed it up enough for it to have the power to make a single-pass knurl.