What's new
What's new

How to Knurl?

Hanz

Cast Iron
Joined
Feb 2, 2003
Location
Casselberry, FL
Haven't done much knurling on my lathe. I have an aluminum handle, 1 1/2" od, and I want to knurl a 2" length.

Do I plunge in, and then feed sideways? All in one pass? I assume a very low back gear rpm, and what about feed rate?

Thanks-Hanz
 
Plunge in quickly, before the part has made a full revolution. Yes, do it in one pass whenever possible, especially with aluminum. Use low RPM, a fast feed (about .025 ipr) and lots of oil. If you don’t have a pinch/scissors type knurler, do yourself and your lathe a favor and get one.

Do a search, both here and at the HSM site. You should be able to find some good information which might be helpful. Knurling without double tracking can be a real pain sometimes.
 
Knurl at the slowest speed you lathe offers.

Do not move the tool until the knurls track
correctly.

Use plenty of cutting oil and keep the chip
brush *away* from the knurls!! You ain't
lived till you've ruined a knurling job by
passing an entire acid brush through the
job!

Knurling is the operation that puts the most
stress on a lathe of all of them. Support
the work as solidly as you can (center, four
jaw chuck) and consider that it will try to
shift sideways into the chuck if that is the
direction you are feeding. If feeding to
the right it will try to open up the center
in the part.

ONe trick I was taught was to shift the knurling
tool *slightly* at an angle to get it to pick
up tracking rapidly.

No matter what, practice on a scrap piece first.

Jim
 
I would point out for the sake of accuracy
here that Doug may be doing his knurling
jobs on a very large, rigid NC machine.
Trying to plunge to depth on a smaller
hobby lathe (and here I count my 10L in that
catagory) does not work terribly well.

Knurling is an extrusion process, the
material is being extruded up into the spaces
in the rollers. Extrusion processes are
often carried out with some kind of lube.

Jim
 
Did I read somewhere that the diameter of the knurl wheel is important in relation to the item to be knurled? It would seem that for the knurl wheel to track it would have to have a diameter equal to the bar being knurled or the bar diameter would have to be an even multiple of the knurl wheel diameter.
 
Yes Jwaggs, that's true but few go through the check to find the best pitch for the diameter. They simply run the knurl and can't figure out why they're getting lousy knurls and chips.

According to my chart, a 21tpi (medium) or 14tpi (course) should give you a near perfect knurl on 1 1/2" stock.
 
I know for a fact (experience and confirmation) that a straight knurl need the right size.

I have been told that a diamond knurl does NOT need the "right" size. I must admit, I do not quite understand why. I also do not have a diamond knurl setup, so I have not tried anything about it.

Anyone care to explain why that is wrong or right?
 
J

I have experimented with calculated diameters and knurling and found it makes absolutely NO difference with a diamond knurl. The knurling wheels on my Eagle Rock scissor-type knurler have lots of slop on their pins (by design I think). I've run these experiments on stainless, mild steels, and aluminum.

The secret to a good knurl in my experience is. . . lots of knurl pressure. I have always knurled with a lot of cutting fluid too, but I'll try it dry and see if it makes a difference.

Like Jim, I may have donated an acid brush or two to the cause


George
 
When I knurl I always leave about 1/8 inch of extra stock to start the knurl on and after I have finished the knurl, face the extra material off and put on an appropriate chamfer. So, if the knurl starts wrong you have a chance to correct it before rolling over on the finished diameter.

When I begin the knurl (using the scissor type knurling post) I first pick up the o.d. with the knurling wheels (on center) and screw the adjustment nut down until the wheels are touching on both sides. Then back off and move over to this extra material on the face,(knurling wheels engaged by about 1/16th on the horizontal) set the wheels into the part just a tad and turn the lathe spindle on and let it go a full turn, watching to make sure the knurl meshes properly . If I get proper mesh I back out the knurling tool and tighten the knurling adj. usually one flat on the hex adj. nut and not losing contact with the part with either wheel. Then, turn the lathe back on and plunge in to the same point again checking for proper mesh and if so begin to manually feed the carriage to the left until my knurl is done. I use copious amount of lube because the knurling tool will pull small flakes off the surface and you do not want those to stay on the part, but float away with the extra oil you are putting on. Not flushing these flakes away will cause them to adhere and give you plating headaches. I never try to finish the knurl in the first pass as you may "overknurl" and cause major flaking. This all requires some practice and BOTH HANDS. Practice, practice, practice, then go for the finished part.

If I have multiple parts I will lock the knurls at a point that gives me an almost complete knurl and do successive parts in one pass.

The knurling tool needs to be square with the part or you will leave a helical spiral on the surface. No problem if the knurl is narrower than your knurling wheels.

Clear as mud, huh ? :confused:

TMD
 
I have been told that a diamond knurl does NOT need the "right" size.
Yep, you're right--size doesn't matter but the TPI does. It WOULD be the same for straight knurls too. It's like matching gears.

If the TPI doesn't fall close to a factor of the stock circumference, the knurl will start to over or under track. The teeth will start to slide into the previous track and cause chips. Makes for an ugly knurl too. Adding oil will just make it slide easier.

Divide the circumference by the reciprical of the TPI (Pitch). This gives you the Pitch applied to the stock. If there's more than about .2 (off zero) in the decimal, you'll get a messy knurl. If the division results in no remainder (.0), you'll get a perfect match.

Cir
------ = Stock Pitch
Pitch


Knurl---TPI----Pitch
Fine----33----0.03030
Medium--21----0.04762
Course--14----0.07143

USING 1 1/2" STOCK--

Fine Example:
1.5 x Pi
-------- = 155.5 (Not a good match- ".5")
0.03030

Medium Example:
1.5 x Pi
-------- = 99.0 (Perfect match ".0")
0.04762

Course Example:
1.5 x Pi
-------- = 66.0 (Perfect match ".0")
0.07143

So for 1.5" stock, a Medium (21tpi) or Course (14tpi) knurl would give the best results. A Fine (33tpi) would cause the pitch to HALF-TRACK (.5) on the stock. (Really ugly knurl)

The same applies to straight knurls.

Forgot to add:
If you want to use a specific TPI knurl (Fine, Medium, Course), then you need to adjust the diameter of your stock for the best fit. Therefor; to use a FINE TPI knurl on 1 1/2" stock, you'd have to turn the stock down to 1.496 or 1.494. This would give you a stock pitch of 155.1 and 154.9 respectively. This falls within the .2 off zero.
 
CCW
Good explanation. That is probably why I have had mixed results with knurling. Sometimes by accident the TPI matches the diameter and the knurl looks great
. Other times it is off and the knurl goes from bad to worse :( .
 
Some time back I started adjusting the diameter of the stock to match the knurls like Ken explains. So far all my knurls have come out good. Before it was hit or miss.
Michael
 
OK, you have my attention. I have been doing some knurling, with mixed results. How do I figure the pitch of my knurls. I have a home-brew clamp type knurling tool and am using .750x.375x.250 bore knurls from Grizzly. The knurls have the diagonal lines that make the diamond pattern when used together in a clamp type tool. Thanks in advance.
 
CCW, by "size" I did mean one that comes out to the right pitch....

Straight knurls are obviously crummy gears. Easy to see the pitch issue.

However, I was told by folks who ought to know that diamond knurls are different and don't have the same sensitivity to pitch.

I didn't see then, and don't see now, why that should be the case.

Maybe it's just more "slop" available in diamong knurls? I don't quite see that either..
 
By size, I was thinking the diameter of the knurls and confusing myself, I guess.

The Diameter of the knurl has nothing to do with a good knurl. It's the Pitch of the knurl that counts. The tooth pitch is what you are using. That's the distance from tooth to tooth. If that distance divides equally into the circumference of the work, YOU WILL GET A PERFECT KNURL.

It's the same principle for ALL knurls JT. Diamond knurls are just two diagonal wheels. Each wheel will run in it's own track. If the circumference of the stock doesn't match close to the pitch of the wheels, you're going to get a bad knurl--Straight or Diamond.

All these wheels do is displace metal--like a press. The chips come from the teeth of the knurl sliding into the previous track. (Hard on knurls too.) I'm just telling you guys what has been working for me. It will take the "Hit-n-Miss" out of knurling. Don't belive me--Give it a try.

I set up an Excel Worksheet with diameters from .250 up to 1.374 (most of my work) and keep it in the shop. When I need to knurl, I look at the chart for the best knurl pitch. It has Fine, Medium and Course columns with the calulations already done. I try to hit ".9", ".0" or ".1" for the best knurl job. If you hit Zero, you should not get any chips and a perfect knurl--Straight or Diamond.
 
Arbo said:
How do I figure the pitch of my knurls. I have a home-brew clamp type knurling tool and am using .750x.375x.250 bore knurls from Grizzly.
Arbo, that's pretty much a standard "size" knurl. I have three diamond sets and a straight that are all that "size". What matters is pitch. My three diamond sets are Fine(33tpi), Medium(21tpi) and Course(14tpi). I looked in the Grizzly catalog (and did an online search) but didn't find their knurls so I have no idea what you may have or what they offer.

You may have to call Grizzly and ask them or Count the teeth. Sorry
 
CCW: I see we agree.....

I wonder what the other guys over on Chaski meant then........I surely understood them to make a distinction.
 
Ken, I did a bit of research last evening. I have three different sets of knurls with different pitch. I counted the teeth on the ones I have mounted now, and came up with 48 teeeth. According to my calcs, that gives me 20.371 TPI. That should give me a knurl pitch of .049088.

SOOOOOO....Assuming a 1.5" work piece

(1.5*3.14166=4.71249)/.049088=96.0008556.
Perfect match? Am I understanding correctly?

Thanks!
 
nobody's mentioned the knurls that cut instead
of displace. they put very little pressure on
the part, but i guess they're not technically
knurling (an extrusion process) not as pretty as
a regular knurl-job with the proper 'crowns' on
the peaks. they just cut a diamond cross hatch
instead.
 
I guess whatever produces acceptable results is an acceptable process. This is not the first time I've heard about relating the work diameter to the knurl pitch.

Personally I don't put much credence in the theory, for several reasons.

For one thing there is the question of how to define the pitch .... is the pitch determined by the spacing at the OD of the knurl, or at the ID of the knurl (which would be in contact with the OD of the workpiece) or at some "pitch diameter" or would it be diametral pitch (which is a definition that makes sense to me) ?

My experience is that there is no need to relate the knurl pitch to the workpiece diameter. If the pattern is not symmetrical and pleasing when applied to a waste portion of the workpiece (that little extra bit that will be trimmed off later), then dig in a little deeper, the process is forgiving and at some penetration of the knurl, satisfactory results will occur.

Of course this is only an opinion based on personal observation - maybe I've been lucky but I've never had a "bad" knurl. I hasten to add that you should follow the procedure that works for YOU.
 








 
Back
Top