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View Full Version : Educate me on knurling, please



brian Rupnow
04-26-2009, 01:47 PM
I want to knurl something on my Craftex lathe. I have been doing a little research, and it seems that the best type of knurling tool is a "pinch" type knurler. The power feed screw on my lathe doesn't work. (Thats a whole other story). Do knurlers self feed or do they require a power feed screw? Any help would be appreciated. I don't want to build a knurling tool, I just want to know enough about them to buy the right thing.---Brian

Paul Alciatore
04-26-2009, 02:24 PM
Scissors or pinch type knurlers usually have rollers above and below the work. When they are positioned properly on the centerline of the lathe, they should be neutral as far as X-Y forces on them but this is an unstable position. In actual practice, some force is needed to keep them in position. The cheaper import tools also have some play in them and this allows odd forces to come into play. Tighten all adjustments as much as possible. Also, if the knurl you are making is longer than the rollers are wide, the tool will need to be moved across the work and this takes force. These forces must be controlled by mounting the tool in a tool post and using the X-Y feeds.

When you say your power feed screw does not work, I assume you mean just that, and the manual feeds do work. If they didnít, the lathe would be useless until they are repaired. Knurling is done with manual feeds, I do it all the time. Iím not even sure if I would want to use power feed. I open my scissors type tool wider than the work and position it as close to the center line as possible. I also position it at one end of the knurl I want to produce. Add lots of cutting fluid and then start to tighten the scissors. If the knurl is longer, I use the carriage handwheel to move it back and forth across the knurled area, adding more cutting fluid as needed. The scissors is tightened a bit after each pass over the length of the knurl until the full depth is reached. Then you can remove the tool by any of several ways; loosening the scissors nut, backing off on the cross feed, or running it off the right end if that is possible.

Get one, chuck up a bit of scrap, and try it. Youíll like it.

brian Rupnow
04-26-2009, 02:28 PM
Thanks Paul---where do I find such a wondrous device, and approx how much do they cost.---Brian

barts
04-26-2009, 02:34 PM
Here are a couple....

http://www.victornet.com/cgi-bin/victor/productlist.html?subdepartments=Knurling+Tool+Hold ers%3A315%2C1084%2C1085%2C1086%2C313%2C317

roughly $40->$50 for import...

- Bart

BadDog
04-26-2009, 02:40 PM
I use power feeds for knurling all the time, but as mentioned, I'm sure manual works.

But don't use cutting fluid. Knurling displaces metal and needs lubricant, not cutting fluid.

And, in my experience, you want to plunge quickly to target depth, don't try to sneak up on it. Easing in is asking for a double track. Might want to practice on a scrap piece of like diameter, or better yet, on an area you are going to turn off after knurling. Find out what depth yields a nice knurl, notice where the hand wheel handle is at that depth (so you don't have to look at the dials), and when ready, just crank directly to that position/depth.

But, "how" to knurl seems a bit of a personal thing, and the specifics of how to feed it in varies quite a lot by person, often accompanied with an almost religious fervor regarding the correctness of that particular method. Lots has been written here on the matter, so a search can yield lots of extra info...

Frank Ford
04-26-2009, 04:58 PM
I use the pinch knurling tool, but I found a way that works better for me than running it on center.

I move the tool over center and tighten the grip until the knurls just touch the work. Then I back away, and tighten the tool down just a little farther than the depth of the knurls - I just guess at the depth.

Then, I run the tool into the work, again until the knurls just touch. Here I'm checking to make sure each roll touches at the same time so they will cut evenly. If needed, I loosen the toolpost and let the rolls find center or raise and lower the tool manually, then tighten up, and recheck.

Now, I'm set to go. I turn on the lathe and run the tool into the work. Since the rolls are very close to pinching the work, there's very little force needed as I press inward.

For me, this system works much more easily than leaning on the knurling tool knob with a cheater bar to get enough pressure quickly. I can get to full depth quickly and have a spare hand to pour the cutting fluid.

mochinist
04-26-2009, 05:22 PM
uh oh a knurling thread :p

Ryobiguy
04-26-2009, 05:36 PM
The cheaper import tools also have some play in them and this allows odd forces to come into play. Tighten all adjustments as much as possible.

You guys have got me thinking - I need to fix up my import scissors knurler. I think many of these import things have to be thought of as assembled parts kit rather than something that'll do a nice job right out of the box.

When I use this knurler as it currently is, I do notice some off axis slop, particularly when I apply infeed pressure (could be sloppy lathe,) and also when starting to feed.

I just took my knurler apart, and the main scissor surfaces where the two halves rotate on each other has a very rough finish. I think I'm going to try mounting it in the 4 jaw and face the surfaces so they have more surface contact (which will also help align the left/right of the top/bottom knurls.)

The bolt shaft/pin that these rotate on proves a super sloppy fit, and it's only 1/2" diameter. While I've got it in the 4 jaw, I just might bore out the pivot hole to 3/4" or 1" diameter, and get a tight fit on a new shaft/bolt (with extra large head) to increase off axis stability. That should help keep them straighter when there is left/right force on them, without locking it down so tight that it can't pivot to find the center.

One thing that always drives me nuts is that the only way that the knurler's square shank will fit in the toolholder is if the knurls are way far away from the toolblock - 3.75". In other words, the pivot bolt for the scissors is about where the normal tool bit edge would be, so I have to move the cross slide waaay back, and sometimes adjust the compound so it can get far away enough from the part.

I'm thinking I might make a custom QCTP tool holder for the knurler. Basically a solid block with a tapped hole that the scissors bolt/pivot shaft will screw into. The hole would be located towards the back (operator side) of the toolholder, so I could switch holders from turning to knurling without having to move the cross slide a mile.

-Matt

x39
04-26-2009, 05:42 PM
uh oh a knurling thread :p
I gather that for some reason this is an unpopular subject. I posted a knurling question last week, and despite something like 100 views didn't get one response.

mochinist
04-26-2009, 05:47 PM
I gather that for some reason this is an unpopular subject. I posted a knurling question last week, and despite something like 100 views didn't get one response.It kinda like the bearing threads, you have a whole board full of self proclaimed experts and each has a way it must be done. They're usually entertaining


what was your question?

tony ennis
04-26-2009, 06:59 PM
What if the diameter of the knurler isn't a divisor of the diameter of the work piece? Does this not make a mess?

John Stevenson
04-26-2009, 07:05 PM
file two teeth off..........

.

Lew Hartswick
04-26-2009, 07:13 PM
I gather that for some reason this is an unpopular subject. I posted a knurling question last week, and despite something like 100 views didn't get one response.
No I'd say it's a very popular subject. I guess about one every week.
:-)
...lew...

tony ennis
04-26-2009, 07:23 PM
(oooooops)

x39
04-26-2009, 07:41 PM
It kinda like the bearing threads, you have a whole board full of self proclaimed experts and each has a way it must be done. They're usually entertaining


what was your question?
Well, in a nutshell I have a quantity (80 pcs.) of 5/8" dia. tp304 ss rods that need knurling over a length of 18". I was asking whether anyone had experience with the Dorian straddle type knurling tools. I ultimately wound up purchasing a Stafford Special Tools unit from MSC, primarily due to the fact that 21 tpi knurling wheels were available in cobalt with a convex form, which I couldn't find for the Dorian tool. I just got the tool on Friday night and haven't had the opportunity to use it yet.

oldtiffie
04-26-2009, 07:46 PM
I want to knurl something on my Craftex lathe. I have been doing a little research, and it seems that the best type of knurling tool is a "pinch" type knurler. The power feed screw on my lathe doesn't work. (Thats a whole other story). Do knurlers self feed or do they require a power feed screw? Any help would be appreciated. I don't want to build a knurling tool, I just want to know enough about them to buy the right thing.---Brian

Brian,

I will try my best to supply and a couple of points of view from credible sources. You can make up you own mind. I hope it helps. I have the same lathe as you do.

The "right" method is the one that works for you on your job on your machine, which is, as it infers, a matter of judgment based on what you are doing at the time. I doubt that there really is a true "one size fits all" method or solution.



Originally Posted by mochinist
uh oh a knurling thread

I gather that for some reason this is an unpopular subject. I posted a knurling question last week, and despite something like 100 views didn't get one response.

x39,
I'd say that its a more "wait and watch the explosion" attitude for some - who may be right - or that hope that they are.

I felt a bit guilty about being one of those "viewers" not answering and so will try to go some way toward correcting my error and "helping out".

As I said to Brian, I have included some links to two publications and the relevant content that might be of assistance. They are different views of the same subject and seem to get satisfactory results for knurling. There may be other tools and other ways.

I hope this helps.

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B3.jpg

brian Rupnow
04-26-2009, 08:09 PM
Thank you Oldtiffie--That information is a big help.---Brian

x39
04-26-2009, 08:53 PM
I felt a bit guilty about being one of those "viewers" not answering and so will try to go some way toward correcting my error and "helping out".
Oldtiffie, no need to feel guilty. By no means can I claim to have responded to every thread I've read, as evidenced by how long I've been a member of this board versus my post count. On the net as in life I'm more inclined to listen than speak. Thank you for the links.

lazlo
04-26-2009, 09:03 PM
I hope this helps.

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_1.jpg
...
http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B1.jpg
...
http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B3.jpg


Tiffie posted the two (opposing) Schools of Thought on knurling:

Tiff's first set of links is the chapter on knurling from Machine Shop Practice, which advocates calculating the diameteral pitch of the knurl wheel, and shaving the workpiece so it's a multiple of the knurl circumference.

Tiff's second set of links advocates the "mash the knurl into the workpiece until it starts tracking correctly". That plastically deforms the OD of the workpiece to make it a multiple of the diametral pitch of the knurl wheel.

Rudy Kouhoupt advocated a third, hybrid approach: feed the knurl in, if it doesn't track correctly, it's because it's not a close multiple of the diametral pitch, so dust off a little off the workpiece, and feed the knurl again until it starts tracking.

Take your pick :)

Glenn Wegman
04-26-2009, 09:19 PM
Tiffie posted the two (opposing) Schools of Thought on knurling:

Tiff's first set of links is the chapter on knurling from Machine Shop Practice, which advocates calculating the diameteral pitch of the knurl wheel, and shaving the workpiece so it's a multiple of the knurl circumference.

Tiff's second set of links advocates the "mash the knurl into the workpiece until it starts tracking correctly". That plastically deforms the OD of the workpiece to make it a multiple of the diametral pitch of the knurl wheel.



I believe that is possibly why knurl wheels come in two flavors to correspond with the above.

Diametral Pitch

Circular Pitch

A huge factor is if you are straight or diamond knurling as straight knurling will require some math to get it right. Diamond knurling, some say the math is the key while others sat it makes no difference.

Glenn

GadgetBuilder
04-26-2009, 09:47 PM
I liked Tiff's last reference:
http://i200.photobucket.com/albums/aa294/oldtiffie/Knurling/Knurl_B3.jpg

It shows a doubled diamond knurl where one side is tracking and the other isn't. I saw this happen and it convinced me that tuning the diameter wasn't the total answer. So I'm mostly a mash it in 'till it syncs guy. Except I've seen that fail... and had to take a few thou off and try again.

So I guess I'm with Rudy - do what it takes to get a decent knurl :)

John

Glenn Wegman
04-26-2009, 10:08 PM
OK, I'll start the fight!

I went for a new set of Diametral Pitch Convex Knurls to see how they worked. I have a dual wheel push or bump style tool and a scissor type tool and fortunately, they both use the same size knurls so one set will do it.

I installed them in the bump style tool using a little J&S Lube (for lubing dead centers) on the axles for lubrication and gave them a try.
http://img.photobucket.com/albums/v647/Fighter1/PC180883.jpg

The thoery is that these particular knurls will work on any sze diameter that is a fractional size of 1/64" increments. The other thing is that since they are convex, they are designed to be fed axially and prduce less spindle pressure as the radius helps the teeth slice into the part being knurled.

For this type of tool I simply turned the bar to a fractional size, touched the knurling tool to it, and zero'ed the dial on the cross feed. The part diameter is the pitch diameter. These particular knurls penetrate to a depth of just about .022" for a full knurl so I moved the tool off to the right of the part and advanced the cross feed dial .022". (this would vary for smaller diameters due to the relationship of the wheel axle centers to the diameter) This would be the minimum diamater of the knurl. Oil the part and run the spindle to achieve 100 sfm and engage the carriage at .010 to .015 ipr feed rate and fed accross the part, reversed the carriage and fed back off. A near perfect knurl with nice shiny flanks!
http://img.photobucket.com/albums/v647/Fighter1/PC180884.jpg

For the scissor tool, you would move the tool off to the side of the part, close the tool up until it just touched something equal to, or measured the minimum diameter of the knurl, center the wheels over the part and you are ready to go. Start the spindle, oil up the part, and engage the carriage. For multiple parts,that will be the way to go for nice consistent knurls.

Well, many may dissagree with the theory, but the Diametral Pitch wheels made perfect sense to me anyway, as a knurl wheel seems like a gear! YMMV :)

lazlo
04-26-2009, 10:38 PM
I believe that is possibly why knurl wheels come in two flavors to correspond with the above.

Diametral Pitch

Circular Pitch

Exactly. And of course the diametral pitch knurls wheels are much more expensive than normal circular pitch wheels, since productions shops don't have time to dork around with getting the workpiece size to be a multiple of Pi.

Duffy
04-26-2009, 10:43 PM
Brian, since nobody else has mentioned it, Busy Bee have a scissor-style knurler. Duffy And yes, I WAS being facetious about Mechanical Design as a career!

chief
04-27-2009, 05:10 AM
Don't overfeed, go slow, and use plenty of lubricant. That's all you need to know about knurling.

saltmine
04-27-2009, 10:45 AM
One thing I've noticed: everybody has their "method" for knurling.
Knurling used to drive me nutz!. I'd knurl one part and it would come out perfect, and then the next part would "double track" and look terrible. I finally cornered somebody who knew the "secret" and beat it out of him.

The secret is circumference. Each cutting tooth of a knurl is spaced a specific distance apart, around the circumference of the knurl. When it's pressed into the work, the circumference of the work must be in multiples of the knurl's circumference, or it'll double track. That's why each knurl is the diameter that it is....to properly knurl common size round stock. If you don't have your part exactly the size that knurl is designed to work on, it will double track...because every revolution, the previous cut won't line up with the knurl. Before I knew this, knurling used to be a frustrating experience for me. Now, if there's any doubt, I measure the part, and do a simple math exercise to see if the knurl is going to track properly. If it won't, I change the diameter accordingly. This works well with common knurls and straight ones.

lazlo
04-27-2009, 11:47 AM
The secret is circumference. Each cutting tooth of a knurl is spaced a specific distance apart, around the circumference of the knurl.

Another vote for the diametral pitch (calculator) method. ;)

Glenn Wegman
04-27-2009, 01:00 PM
Just a note:

I just boinked the test piece in my above post for hardness and it is RC25 as knurled. I'm even more impressed at the results now! I had just grabbed it out of the scrap bin to test the new knurls and it seemed like it had a little temper to it when I turned it down to size, but I never checked it.

Glenn

brian Rupnow
04-27-2009, 05:19 PM
Well Damn!!! That was almost too easy. I rushed off to BusyBee Tools at noon and paid $25 (on sale) for a scissor type knurler with a 5/8" square shank. I set it up in the toolpost of my lathe, --it appears that the shank of the knurler doesn't really have to be centered horizontally on the chuck centerline, as this type of knurler is somewhat "self centering" due to the pivot points on the upper and lower arms---but it should be "fairly close". I took care to align the upper and lower knurling rolls with the center of the chuck vertically (when viewed from above). I chucked up a length of 1" round aluminum scrap and closed the knurlers via the single adjusting screw untill they just "kissed" the outer diameter of the round aluminum, then backed the compound rest towards the tailstock untill it was just clear of the part I wanted to knurl. I closed the knurl adjusting screw by about half a turn, squirted everything with some used motor oil, set the machine for 115 RPM, said a quick prayer to the machining Gods and turned on the lathe. I advanced the knurling tool slowly towards the workpeice (away from the tailstock) untill I could see both of the knurling wheels begin to rotate from contact with the revolving workpeice, then advanced the feed (away from the tailstock) untill the knurl had completely passed over the area I wanted to knurl. I then backed it off and usd an old paintbrush I have to clean the oil and swarf away. It looked good, but not quite deep enough. I advanced the knurling adjustment screw another 1/4 turn (this seems very sensitive--a little turn makes a big difference in knurl depth). and repeated the process.---and Voila---It worked. I am sure that ther are a thousand things left to learn about this, but for a first time event, I was surpised and pleased at how simple it was.---Brian
http://i307.photobucket.com/albums/nn294/BrianRupnow/KNURLING002.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/KNURLING001.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/KNURLING003.jpg

tony ennis
04-27-2009, 09:11 PM
Sweet. I'm machining vicariously. Please keep posting pictures.

saltmine
04-28-2009, 04:23 PM
Quoted from, "Machine Shop Secrets": "A proper diameter to knurl is any diameter that is a multiple of the spacing, or distance, between the teeth of the knurling tool divided by Pi (3.14159). The relationship is the same wether the knurl is diamond or a straight knurl. However, you must measure the spacing of a diamond knurl's teeth along the axis of the part or roller for the relationship to hold true."

With this information in hand, every knurl I make now is a good one.