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Dave the Nave
11-21-2001, 08:50 PM
Anybody got any tips or suggestions on knurling? I seem to be having tremendous difficulty knurling a 1.5" dia.aluminum(6061-T6)bar on the lathe,even though I have the rollers leveled up with the work piece,I still can't synchronise the rollers to produce a good diamond pattern.I've lost about 10" of stock so far due to trial & error.Any advice is appreciated ,Thanks.

Randy
11-21-2001, 11:36 PM
There's a long thread on knurling in the Third Hand forum, last added to 8-31-2001. The search function didn't work for me, I found it the hard way, but this should help you find it.

George Hodge
11-21-2001, 11:36 PM
Dave,knurling can be tricky! Lots of lubrication is vital,as is having the right size diameter knurls and the right pair. Home Shop Machinist had an article on knurling just lately,can't remember which one.I lend my magazines to several friends and don't have them here right now.Try going slower,more pressure.
By the way,a "Nave" is the central aisle of a church.???

crypto
11-21-2001, 11:42 PM
What size lathe? Is your stock supported by center? What RPM?

You may receive as many suggestions as the number of fleas on a junkyard hound. Everyone has a pet method which sometimes works and at other times is merely an embarrassment. Here's a tip from a jobshop machinist who has to make a good knurl everytime-Angle the knurls 5 t0 10 degrees. Sink the knurls into the job full depth, 40 to 60 thou, on the very first turn at very slow rpm, as soon as tracking is satisfactory start the feed. This works for him and keeps his boss happy.

Thrud
11-22-2001, 12:12 AM
Dave,

P=dimetral pitch of knurl
D=nominal diameter of knurl=t/P
t=# of teeth on knurl =P x D
CP=circular pitch on nominal diameter = pi / P
CPM=circular pitch on major diameter = pi x D / t
Dm=major diameter of knurl=D-(tQ / pi)
Q=CP - CPM = tracking correction factor

This will allow you to calculate the proper diameter to make the work to be knurled. More detailed info in in Machinery's Handbook under "Knurling"

Other factors could be worn out knurls, too much slop in the knurling tool, loose pins, missing thrust washers, and poor lubrication.

Good luck

Dave

halfnut
11-22-2001, 12:23 PM
Dave,

Thrud's put up the formulas and such.

Just can't expect to knurl any particular diameter because of the pitch of the knurls, have to do the math. Then knurls vary just a bit, have to find the sweet spot of plus or minus a few thous of calculated dia.

I never had much problems knurling with the old Armstrong floating knurling tools. Do the math on these old tools and lo and behold, the pitches were such that they would knurl inch fractional sises. Now with the Aloris types we have to prepare special diameters for the knurling.

Progress right, probably got to do with metrics, it's a conspiracy I do believe.

Other fellers have some good advice, and I better go and get cleaned up to eat turkey.

Dave the Nave
11-22-2001, 02:29 PM
I guess there is more to knurling than I had anticipated for it to be.But before I get out the calculator and do the math,I'm going to try tilting the tool 5 deg.using more pressure and flooding with oil as was previously mentioned here.I'm using a LeBlonde Makino(14x60)25 h.p.servo shift lathe,running about 125 rpm.So the torque and the rigidity are a plenty for knurling.The piece is 6in.sticking out of the chuck and supported w/live center.Oh, one other thing(not to change the subject too much here)Back in my high school days I was elected team captain in phys. ed.and my coach(who had a Brittish accent)called me "nave"since I was the focal point of the team and it rhymed with Dave.Other than" the center isle of a church",I've allways thought that a nave was an English version of a coach.That sorta stuck with me ever since and being that there are other Daves on this bulletin board,I thought I'd be a little creative.Now getting back to knurling,would'nt it be awesome if there were such a tool(if it does'nt allready exist)that would "cut" the diamond pattern rather than form it under pressure?Thanks again ,folks.And have a wonderful Turkey day.

Neil Butterfield
11-22-2001, 03:42 PM
I agree knurling is a subject that has not been explained well in most machining articles and so-called textbooks. Through experimentation, and a lot of terrible looking knurls, I finally found a system that works for me.

Calculating the "optimum" diameter is the first step. Check the following Home Shop Machinists articles:
May/June 2000 p.44
May/june 2001 p.56
and/or the following Projects in Metal articles.
Aug. 1997 p.22
Aug. 1998 p.44
Dec. 1998 p.44

If you don't have access to these contact me and I'll give you my condensed version of the above formulas. It's quite easy, especially if you have a calculator.

I got fantastic results on the following knurling job. I used a 3/4" dia. knurl, 25 Teeth, Work dia. 1.00" Cold rolled Steel.I used a scissor type knurling tool (180 degree opposed knurls). Ran my little 9" South Bend in back gear at 76 RPM and a feed rate of .0244" per rev. I assume a plunge type knurl will also work but it may take more passes.

It took me approximately 10-12 passes as follows to get a nice diamond shape.

I engage the Knurl on the tailstock end of the work by tightening the scissor tool nut about a quarter turn. Setting the tool at a slight angle, 2 degrees or so helps. Engage the power feed and take a pass, in my case I was knurling for about 3". At the end of the pass (the 3" in my case) stop the spindle, reverse the feed lever, start spindle and return to the start position. Never disengage the knurls. Reverse the feed for the next pass, tighten the scissor nut another quarter of a turn, or so, and repeat with another pass right to left, stoping the spindle at the left end of the 3" pass, reverse feed and return to the start position. Sometimes I had to relieve the tension on the scissor nut on the return pass, the left to right pass, You do not need to be "knurling" on this return pass (no need to put that kind of pressure on the tailstock) the "knurling" should be done when feeding toward the headstock.

Repeat this process as often as is necessary to get a knurl you are happy with. As I said earlier, it took me about 10 or 12 passes to get a nice knurl.

Yes, I used lots of heavy cutting oil also.

I've never seen a knurling article described in this much detail. I wrote my proceedure down for perfect reference for the next time I do some knurling. I'm a hobbist (sometimes for pay) machinist also and I don't knurl that often. My memory isn't what it used to be so I've found that recording my proceedures in complicated machining operations saves a lot of frustration next time I tackle a similar task.

I hope this helps.

Neil Butterfield

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Neil

crypto
11-22-2001, 04:02 PM
Assuming that your knurling tool is in good shape then here is some detailed info (I have a 14" Toolmaker Servo LeBlond almost the same as your lathe). Start at lowest rpm 30-40, jam the knurls full depth into work and check that proper tracking is achieved by the first complete revolution. If knurl is not satisfactory back off and start again. Keep lubrication on the knurls and work. (Important to keep the knurls and their pins lubricated or pins will be damaged by pressure of full depth cut). Then engage feed and speed up the rpm to proper speed.

The formulas are needed for production mfg. of knurled pieces where hundreds of pieces must be made without incurring expensive scrap costs. Job shops will use the same beat-up knurls for all diameters. Taking time to figure formulas would guarantee a rapid exit from that shop.

Hope this helps. Incidentally the prettiest knurls that I have ever seen, like knurls on my old Contaflex, are illustrated and described on Pg. 179 in The Model Engineers Workshop Manual- Geo. H. Thomas. This book (available from Tee Pub.) should be in everyone's bookshelf who loves the trade. Contains much knowhow accompanied by beautiful photos and frank descriptions of triumphs and errors.

snorman
11-22-2001, 06:05 PM
I'd go with crypto's jobshop machinist. It seems to work for me too.

Steve

jkilroy
11-23-2001, 05:09 PM
Check out this link...

http://www.accu-trak.com/engineering/blank_diameter_selection.html

Also this page is good...

http://www.doriantool.com/Knurling/technical_information/knrl_bxIII.pdf

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James Kilroy

[This message has been edited by jkilroy (edited 11-23-2001).]

MarshSt
11-23-2001, 07:49 PM
I am using some 5.5" 4140 knurled wheels for a project of mine at work. Our tooling dept. is building the wheels so I'm not doing it myself. The first few sets of wheels, 2MM diamond knurl looked terrible. The tracking was all over the place, some of it operator error. We ordered up a couple sets of crown wheels (not sure of the exact terminology)from Accu-Trak. Their holders and wheels are really inexpensive compared to the other stuff we tried. The wheels made perfect straight pattern knurls on the same material. Different machinist, but I think the wheel design had a lot to do with the success. The design lets you set the wheel to full depth before you start onto the part. The full depth start would probably help with standard wheels but you would have to bury the wheels into the part first.
The knurling tools that hold the wheels at an angle off the part centerline, (2 straight pattern wheels at 30 degree angles to make a diamond knurl), are suppose to cut the knurl as opposed to forming it.

Steve

George Hodge
11-23-2001, 11:13 PM
Dave,somewhere in the piles of old shop magazines around here,I saw an article about making multiple start threads.It said for a nifty looking part to be gripped,Thread both right hand and then left hand on the part with a 60deg.threading tool. I've never tried it,most of my stuff doesn't need the pretty knurling applied
George

kap pullen
11-27-2001, 10:49 AM
a "pinch" knurl works best. There is no load on the spindle or center with this tool.
With a regular knurl, start the knurl on the corner of the part,with only about 1/8"
of knurl engaged. Go in to full depth fast,
engage the feed (.010/.020).
Run plenty of coolant, soluable oil works well. The coolant flushes out tiny flakes of metal which will leave rough finish when rerolled into the surface.
I angle the knurl a couple degrees to give clearance to the back of the tool.
good luck
kap pullen