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A Problem with Knurling

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clevinski

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#1
Hello, All,


I made a couple of aluminum knobs yesterday, and wanted to put the coarsest, straight knurls I could on them. My problem is that, when done, instead of pretty, smooth knurls, the material surface itself looks pitted and chipped, as you can see in the photo below. I have made several nice aluminum knurls in the past, but used the finer wheels and those were cross-hatched, not straight.

I was knurling aluminum, using the coarsest, straight knurling wheels I have (14 lines per inch). I have a "pinch-type" knurler from LMS; see below. I cut the outer diameter of the part to 0.978 inches, which makes the circumference in inches evenly divisible by 14, so that the knurl lines should line up after a full revolution. I started with a very light pass and with the wheels about 50% engaged, and moved slowly across the part by hand. I used old-school, dark cutting oil (mineral oil) as the lubricant and oiled the crap out of the surface and the tool during the process. I wiped the part after each pass and used a chip brush, but it wasn’t too effective at removing all the aluminum particles. You could see that the oil was basically a mix of thousands of small aluminum particles and the dark oil. In fact, after each pass, the lubricant was more silver than dark, in spite of my adding oil as we went. After each pass, I would tighten the knurling wheel some more and reverse direction. I was using a Real Bull 7x14 mini-lathe from Big Dog Metals.

I suspect the issue is that there was too much aluminum powder from the knurling process in the lubricant, and it essentially ground the knurls, but I don't know what to do about that as I was already oiling it very heavily.

Any suggestions would be appreciated.


Knurls w Bad Finish.jpg
knurler.jpg

Knurls w Bad Finish.jpg knurler.jpg
 

basalt

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#2
Possibly try compressed air and coolant, another thing we used to do was tip the knurls slightly so they were cutting mostly on the leading edge as opposed to the full width--feeding along of course. I suspect the oil is acting like glue, I've never used oil when knurling aluminum.
 

rgray

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#3
Lots of pressure and one single pass over it works better for me than trying to be nice to it and adding pressure over multiple passes.
I don't use any lube on aluminum when knurling it either.
I have the same knurling tool. Much of the time I will put it over the part and tighten it down hand tight then retract the cross slide turn the tool another 1/4 to 1/2 turn tighter then advance the cross slide back to centered over the part and then run the lathe. Vary the look of long knurles by changing the carrige travel speed.
 

eightball

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#4
It could be that you just went to deep also. I have done the same thing on brass b4. The knurl would look great then id feed in a bit more and my finish would strart getting flackey.
 

Tom Griffin

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The pitch of the knurl has to go into the circumference of the part evenly with coarse knurls. Otherwise the knurl will overlap and create a mess like you are seeing. It's not as critical with fine knurls because they tend to index without issue, but coarse ones can be a pain. For example: If you had a 1.512" diameter part, the pitch of your knurl (1/14=.071) would go into the circumference of the part 66.5 times (pi times 1.512 divided by 1/14 = 66.5), so you would need to adjust the diameter up or down one half the pitch to 1.500 or 1.524 to get a good knurl. It doesn't seem like much but it can make a huge difference in how your knurl will turn out.

Tom
 

clevinski

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#6
Thanks, Guys!

My bad, I guess... I thought that you always used lubricant when knurling anything. Come to think of it, when I knurled the finer, diamond pattern parts, I used WD-40, which is very thin and light. This dark cutting oil is very thick, so maybe I should try again dry. I assume that you guys use a cutting fluid when knurling steel?

Eightball, I think you're right, and I went too deep at the end, but I would check the appearance of the knurl after each pass and the rough surface was always there. You know you went too deep when the knob doesn't want to tighten any more.

Thanks for all the input, guys! I'm going to use these for now, since they're parts for a lathe stop I'm making, but I will probably remake them in the future on a slow machining day...
 

clevinski

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The pitch of the knurl has to go into the circumference of the part evenly with coarse knurls. Otherwise the knurl will overlap and create a mess like you are seeing. It's not as critical with fine knurls because they tend to index without issue, but coarse ones can be a pain. For example: If you had a 1.512" diameter part, the pitch of your knurl (1/14=.071) would go into the circumference of the part 66.5 times (pi times 1.512 divided by 1/14 = 66.5), so you would need to adjust the diameter up or down one half the pitch to 1.500 or 1.524 to get a good knurl. It doesn't seem like much but it can make a huge difference in how your knurl will turn out.

Tom
Hi, Tom,

Thanks for your comments. Yes, I know how critical the diameter is from my research before I started knurling. I actually made an Excel spreadsheet for the exact diameter for knurling each common, nominal diameter material when knurling with the three different line pitch wheels that I own. That's why I made this part 0.978 inch diameter. (Well, 0.9777 would have been more accurate, but I figured accurate to .0003 would be close enough.) .9777 x pi = 3.0715. 3.0715 inch circumference X 14 lines/inch (same as dividing by 1/14) = 43.001 lines per revolution, an error of only 0.1%. I would think that was accurate enough, but this is the first time I've tried to do a coarse knurl, so I could be wrong. What do you think?
 

stern

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#8
Not sure if its just me, but last week I knurled alluminum for the first time (foot pegs for a CX650) and even though I set the diameter right, it did a similar "powdering up". I tried again with coolant (water based milky stuff) and it made a huge difference, as i used a spray bottle (with a thin stream) to "blow" the crud out as it went.
 

eightball

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#9
I like to use my kool mist system when knurling. Even though i have coolant on my lathe, I can set my koolmist nozzle to blow directly at my knurl and still see what im doing.
 

Tom Griffin

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#10
Hi, Tom,

Thanks for your comments. Yes, I know how critical the diameter is from my research before I started knurling. I actually made an Excel spreadsheet for the exact diameter for knurling each common, nominal diameter material when knurling with the three different line pitch wheels that I own. That's why I made this part 0.978 inch diameter. (Well, 0.9777 would have been more accurate, but I figured accurate to .0003 would be close enough.) .9777 x pi = 3.0715. 3.0715 inch circumference X 14 lines/inch (same as dividing by 1/14) = 43.001 lines per revolution, an error of only 0.1%. I would think that was accurate enough, but this is the first time I've tried to do a coarse knurl, so I could be wrong. What do you think?
Perhaps I should have read the entire thread rather than just look at the pic. :p

Yes, the diameter you chose should work fine. What type of alloy are you using? Unless it's cast, it should knurl fine provided you use some lube (I like WD-40 on aluminum), keep the chips clear and don't go too deep.

Tom
 

clevinski

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#11
Stern, Eightball,

Sounds like air is an important component when knurling aluminum. I'll try it next time; thanks!


TomG,

No problem... I think I *did* go too deep in addition to not clearing out the powder. The aluminum is 6061.
 

Metalmann

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#12
I've done quite a few knurls going into full depth pressure, automatic feed, and mister method; even on Aluminum.
 

Frank Ford

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#14
Try a SINGLE

Sure you're not getting some double-tracking? I've had that problem when I've used a two-wheel tool for straight knurling. A single wheel works best for me for this kind of knurl.
 

clevinski

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Re: Try a SINGLE

Sure you're not getting some double-tracking? I've had that problem when I've used a two-wheel tool for straight knurling. A single wheel works best for me for this kind of knurl.
Hi, Frank,

I am certainly getting some double-tracking, which is another issue. I'm beginning to learn, from answers here and on one other forum, that no one seems to be very successful with straight knurl tracking with a pinch-type knurler. Makes me wonder why they provide three sets of straight knurl wheels with the tool... A single would eliminate the problem with both wheels having to sync up with each other. For a pinch knurler, someone suggested using one knurl tool and one sacrificial plastic roller, which they had done successfully.

But that said, in my limited experience, double-tracking doesn't cause the existing knurls to look all... what's the word? Chipped, maybe? Or broken? I think that issue is that I should be using flood coolant or air to keep the powder off the work as it's being formed. I'm going to have to experiment more with it. However, since I can't seem to sync up the straight knurls anyway, I think I will go on to more productive activities and stick with diamond knurls for now.
 

Hawkeye

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#16
If you think about it, when you're doing diamond knurls, you're not using two wheels. You're using a pair of single wheels. One for each 'slant' of grooves. The bottom wheel isn't being asked to fall into 'track' with the top wheel. each is forming its own grooves. I don't have any straight knurls, but if I get some, I'll try to remember this and use a plastic roller.

I had a diamond knurl job jump to a double track once, but it was a pretty accurate half-spacing. A set of medium knurls gave me a very nice fine knurl. Take a look at the ring holding the sector arms on the rotary table.
P6170062b.jpg

P6170062b.jpg
 

clevinski

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#17
If you think about it, when you're doing diamond knurls, you're not using two wheels. You're using a pair of single wheels. One for each 'slant' of grooves. The bottom wheel isn't being asked to fall into 'track' with the top wheel. each is forming its own grooves. I don't have any straight knurls, but if I get some, I'll try to remember this and use a plastic roller.

I had a diamond knurl job jump to a double track once, but it was a pretty accurate half-spacing. A set of medium knurls gave me a very nice fine knurl. Take a look at the ring holding the sector arms on the rotary table.
View attachment 55521
Hawkeye,

Yes, I agree... diamond knurling is actually two separate single wheel's whose line position relative to each other is irrelevant.

I'm not too familiar with rotary tables, and maybe I'm missing it, but the only knurl I see in this photo is the one next to the graduated collar on the hand wheel in the bottom, left side of the photo. Is this the one you're referring to?
 

Linghunt

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#18
Great thread, I swapped Oil out for Kool-mist. Boy what a difference. Cleaning out flakes in kurls not a fun job.
 

rzbill

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#19
I asked on a different knurling thread but did not get much response. I'll try here.
I have a two wheel (diamond pattern) bump knurling tool (Phase II). Came with lathe.
In order to identify the pitch, I counted the teeth on the 3/4" wheels.

To my surprise, one had 39 teeth and the other had 40. That was unexpected even though as was stated earlier the two wheels have no registration relationship. Pitch math did not come up with an integer value for either. Comments?
 

Linghunt

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#20
I would 1st have the same pitch on the wheels, knurling is tough enough with correct setup. Which pitch to choose there are lots of info about calculating it.
I made up a excel sheet for it for the pitch options available from Acccu-trak.

Your welcome to it.

Not sure just how critical it is, but can't hurt.

Oil for stainless and kool mist for aluminum was my new lesson.

Here is a picture of some motorcycle parts, Made those with Oil.


 
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rzbill

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#21
Rearsets? Forward controls? Or hand grips for tough guys? ;)
 

Linghunt

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#22
Not sure, I know they went to Perth, Australia. Link has pictures of the bikes.

Custom bike builder had issues with local chip makers. Now he goes to across the world to Linghunt spear tip weapon shop. Honored to have my parts on his bikes. He draws great sketches btw for what he wants. Some of the part challenge me out of my comfort zone, but that's good

http://www.linghunt.com/Projects/CustomMotorCycle/MotorCycle.html
 

rzbill

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#23
Bike terminology. Looked at your web page and see that the pics posted here are forward controls. Interesting pics from your customer. Not my style but I appreciate the workmanship that went into the scratch built bikes.
 

Linghunt

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#24
I took some pictures of my manual setup before I broke it down. FYI. I sure like that big Aloris holder. Got it for a deal on Ebay years ago.

After chasing a good knurl for years, besides proper alignment and proper feeds, the knurl wheels themselves seems to be the a huge part of it. Those china made wheels I tossed them. Look at them with eye lobe.

Let me look for a video of CNC knurling. I might have one. That huge job was actually easy for knurling, other aspects of it were more difficult. Knurl was my fear taking it on. zero experience with programming for knurl.










 
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