Knurling Tools?

That doesn't make any change. There are other knurling tools that look more like a C-clamp. They have a knurling wheel on top and bottom of the workpiece and pressure is only applied by a screw of that tool. Don't know if they really work. At least, the have very little load on the lathe.

Made my own knurling-holders. Two different ones for one wheel, and one for two wheels (not the C-clamp type).

Knurl wider than you need and cut off the ugly part.

I make it that way: Slow speed. Something like 200 RPM for 30mm diameter. Feed in to some extend and then feed sideways. On the left end, feed in, feed to the right ... about 4..6 passes back and forth make a perfect knurl. By any means, you need cutting oil! Better would be coolant to wash the fine swarf away. After that, I go over it with a wire brush.

Nobody knows that. So sometimes it doesn't work at all. In this case, I start knurling at the very edge (just a 1 mm wide knurl) feed in until it works and then feed sideways. But the load to the lathe is really big that way.

HTH, Nick

The scissor type kurling tools are certainly much kinder to the headstock bearings than the standard "push-in" type; they also make it possible to knurl thinner material.

Its tempting to think of knurling as a variation of gear cutting, where you *have* to ensure that the circumference of the workpiece is an integer multiple of the knurl pitch, but it doesn't work like that. Once the pattern is formed, extra pressure simply deepens it, even though the effective diameter of the workpiece has changed. Why is this? Obviously, once the pattern has formed, its easier for the knurling wheel teeth to slip a little so as to follow the existing valleys rather than form new ones. This observation is the key to successful knurling. Press the wheels very firmly into the workpiece at the very start. That way the wheels create nice deep valleys immediately, and when the workpiece has revolved sufficiently for the wheels to meet the previously formed valleys, they fall in step and reinforce the pattern. So, the secret to successful knurling is to press the wheels in good and hard right from the start, and use plenty of lubricant to allow for the slipping - it always works for me. As others have said, it helps to start the knurl near the edge, about 1mm wide. This makes it easier to establish a good deep pattern that, once formed, will be maintained as the tool is moved sideways.

You will not accomplish much by going to a single wheel type knurl. With it, you still have to pound the knurl into the work. You will just have to do it twice, once for each side of the diagonals. Going to a scissor or squeeze type takes the load off the lathe, and will make life a little less miserable, at least as far as knurling goes. There have been quite a few designs published in the model engineering press, and anyone with a bit of metalworking experience will be able to make a working one from looking at a picture.

Knurling does not often work well if approached with any modicum of caution. The bold do well, for the most part. Get the tool in hard, and keep the pressure on, and the knurl tends to work fairly well without having to resort to trying to figure whether you have the exact correct diameter, etc. Hesitate, and all is not lost, but most of the time...

Cheers Trevor Jones

A website with drawings.

Cheers Trevor Jones

GL

>

Probably.

But Nick mentions that if it won't work, he can drive the tool harder into the work until it does. That suggests that the tool will slip over small errors, but with large errors you have to drive it in harder, which means the working diameter (like the minor diameter of a thread) is made smaller. So eventually it will either work, or break the tool.

-adrian

As to why it does`nt mash up the surface. I think thats one of lifes mysteries. Do remember that these things form not cut (I think) so you need to clean up each end of the knurled surface.

That's what is happening. When I played around with knurling, I calculated the right diameter and ... I got the worst result possible. :-) Why? Because I would have gotten zero slippage when readily knurled, but not when starting.

The tool won't break. But I repeat the trick if you can't get it started (as soon as it started right, it won't loose the groove): Do not start with the full width of the knurling wheel but with just one 1 mm or so. Push it in until it works. Then feed sideways. If that load is too much, you can even retract the wheel a bit. It will use the good "gear" as a guide.

Search for knurled parts in your drawer and look close to them. You will discover that most of them are knurled bad. Just some "minor scratches". Only then, it is important to have the right diameter. But if your really knurl it perfectly (getting small pyramids) it doesn't matter. It's only the starting technique.

Nick

But, to be fair, I often failed on my small EMCO Compact 8. On my new and much bigger lathe, it's almost just brute force.

Nick

I made a small tailstock mounted knurling tool for my Lorch LAS, This is a scissor type tool with two 10 dia wheels. each mounted in it's own arm, these are pivoted on a plate with a M 1 shank on the back. An M 5 screw applies pressure between the arms. This will knurl a 4 mm diameter, it would do smaller if I had taken more care with the positioning of the arm pivots - the contact point of the wheels is slightly off centre due to me rushing the making. I always use a scissor type knurling tool on the larger lathe and find that lube oil works better than cutting oil/coolant. Mark G.

I'll take my wild guess. The typical knurling tool has two rolls putting a pattern at angles to each of the rolls. So ridges are formed that the next wheel doesn't have to track which sets up ridges that the first wheel isn't forced to track though the tendancy is home in where each wheel finds its own pattern.

Wes

I hesitate to diasgree with so much expertise but I believe the diameter of the work actually is important.

When I started I bought one of the Indian made scissor type knurling tools and got lousy results from it. I decided there were two problems - the alignment of the top and bottom wheels was sloppy because of play in the bearings, and the random diameter of the work meant that it is a matter of luck whether the knurls hit the work in the same place on each revolution. It was also a pain to change knurls as the pins have to be punched out.

I built the knurling tool holder from Hemingway's kit

which holds the two knurls in perfect alignment and prevents sideways play. I also found on the web (can't recall where) a neat little C-programme which runs in a C: prompt window and calculates exact dimeters for knurling. You input the diameter and number of teeth on the knurl, and the nominal diamter of the work and it calculates the exact diameter (usually pretty close to nominal) to which the work is machined to get an exact knurl pitch.

Wit this setup I get good knurls and am very satisfied. I discussed the problem with a expert toolroom engineer at work and he told me that diameter is important though he gets perfect knurls by trial and error, machining of a few thou until the pitch is correct.

But it also works with single wheel knurling or making parallel impressions (don't know how that is called).

Nick

All this talk about exact diameter is a load of s**te.

That formulae setup was dreamt up by some armchair wizard who had nothing better to do with his time.

First off the theory is all wrong to start. All this crap about D x pi / P = Nc is wrong because a knurl wheel is a gear and gears are made to mate on their Pitch Circle Diameters not the OD or the root so if you are using the wrong formulae how can you get a correct job.

I'll prove this two ways - first theory based on D x Pi etc. Lets take a 2" bar and a knurl that has teeth measured 30 thou apart.

So 2" x Pi = 2 x 3.1416 = 6.2832" Now divide 6.2832 by 0.030" [ the pitch of the knurl ] and we get 209.44 teeth. Perfect we now have a doubled up knurl [ big fanfare etc ] but we haven't taken into account the DEPTH of the knurl. You do need a depth don't you ?? it's not just etched on the bloody surface, so we will say that this 30 thou pitch knurl has a depth of

15 thou, that's on radius so it's a total depth of 30 thou on diameter.

So lets do the figures again using the root of the knurl, because that's where the OD of the knurl wheel will finish up.

2" - 0.030" [ the depth ] x 3.1416 [ pi ] = 1.970 x 3.1416 = 6.1889 Now divide this by 0.030" [ the pitch ] and we get 206.30 teeth

So we have 206.30 teeth at the root but 209.44 on the OD Three teeth difference, which proves the formulae is crap because at some point as you wind in you go from 209.44 to 206.30 teeth. Metal is plastic and will 'flow', if you only had to go once round you would get errors but knurling is a continuous rotating process and it levels out any differences, hence the three theoretical teeth.

Second method - practical. Practical for anyone not fully understanding the word is defined by one having to get up off ones arse and go out into the workshop and get ones hand mucky.

Practical - a useful word to remember.

OK first off this is a knurl test bar to prove the formulae is just an old wives tale.

This is just a steel bar about 1" in diameter with a skim taken off it to clean up. Then just using the dials I have stepped this in 5 thou steps [ diameter ] so the start end is 25 thou thou smaller than the chuck end.

I have no idea what the diameters are and the steps are only roughly 5 thou steps. The idea is I don't need to know because it's not relevant.

Now starting at the small end we do a straight knurl and run up to the chuck, under power, same setting.

This is the finished job. You can see the steps. You can also see that even though there are 6 different diameters of God knows what size all the knurls have come out good.

Now if that formulae old wives tale was correct at least some would have come out cack handed but they haven't because going back to the theory buster the difference between ONE tooth is only 1/3 of the depth so at some point infeeding you have to hit that and once you do the flow of the knurl will guarantee that it carries on.

Now can I get back and get some bloody work done ??

-- Regards,

John Stevenson Nottingham, England.

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Sarcastic question: Is the result given true when you start to knurl or when you have finished knurling. Or half way through?

Nick

Work? That post was written with all the passion of one who had just returned from the boozer ;)

Stu G (Just returned from Tesco if you were wondering)

I have to agree with John. I find that the success of knurls is more dependant on the material than anything else. I always use a scissor style knurler as I was taught that the other style put too much force on the headstock bearings.

I start with half the wheels width on the job and progressively screw the knurl wheels together until the correct pattern starts to form, then slowly progress along the job. The lathe is turning at a very slow speed, and I use lots of oil on the knurl wheels.

The knurl wheels are squeezing the material to conform to the shape, not cutting, no significant quatity of material is removed.

AWEM

Well he'd obviously just come back from a bar - knurling a bar, that is

Regards, Tony