Straight Cut Knurling Problem and Plans For A Bigger Lathe (Colchester Master 2500)

[stephen thomas]

It would help anyways, by reducing the tool pressure,
so the OP could use both bump or cut.

Can you post a link to a scissors type cut knurl?

BTW, i have, & have used for production, multiple types of scissors type compression knurls, which are what your original link shows.

Thanks,
smt

 

[Beauvais]

After some testing last night, I think the cheap chuck could be the biggest cause of the problem. I measured the part, chuck and saddle and found that the part very easily moves, with the machine off I pushed the knurl into the part and could get 0.1 to 0.2mm deflection. The saddle does have some slight 'play' when lifting from the front side but it takes quite a bit off force to lift, there is no adjustment by standard, I could skim some material off the fixed gib but then I still have a cheap chuck. I also tightened the spindle bearings slightly but that didnt help, the spindle was quite easy to turn and I had wanted to try tightening them for while anyway.

I could perhaps buy a quality chuck, straddle knurl tool and do modifications to the saddle, but ultimately Its still under powered and not long enough for what I need it for. For reference, I need to make a part thats 750mm long and around 26mm wide with 15-20mm of knurl at each end in 4140. With this lathe I need to remove the tailstock, rotate the top slide 180deg to be able to take off material (30mm original dia) so it can then fit through the 26mm spindle bore to be able to drill and tap the other end.

Here is a test I did with a vcmt 0.2 radius finishing insert at 0.5mm doc. Thats 0.04 over 35mm length.

 

[Beauvais]

All standard practice/cure for compression (or "bump") knurling.
Should not be necessary for cut knurling.
No one is addressing that point.

Or is the OP's tool not a cut knurl, as listed?

smt

Its from Quick Hommel+Keller. They only do cut wheels in the dimension the tool I bought specifies. Although it feels kinda dull, I have no experience with other knurling tools so I dont know what to expect.

https://www.hommel-keller.de/en/quick/​

 

[stephen thomas]

Its from Quick Hommel+Keller. They only do cut wheels in the dimension the tool I bought specifies. Although it feels kinda dull, I have no experience with other knurling tools so I dont know what to expect.

https://www.hommel-keller.de/en/quick/​

So it is some version of the 601, cut only, single wheel, RH tool?

Did you buy it new or second hand as pertaining mostly to the cutter?
Since they also make compression/form knurls, was it shipped with the correct cutter?

What is the hardness of the workpiece?
Are you asking too much of any knurl process on hardened steel?

smt

 

[Beauvais]

So it is some version of the 601, cut only, single wheel, RH tool?

Did you buy it new or second hand as pertaining mostly to the cutter?
Since they also make compression/form knurls, was it shipped with the correct cutter?

What is the hardness of the workpiece?
Are you asking too much of any knurl process on hardened steel?

smt

Yes it is definitely the correct wheel as there are no form wheels with the same dimensions. It was new in sealed packet, dont think it could of been a return.

Its 4140, I called up the company I bought them from just to double check just now and they say it should be ok. They sent Quicks own speeds and feeds chart and they call for a faster feed rate and rpm than what accu trak say, I have tried high and low rpms already though. This far in I dont mind doing more tests although a bit tedious and a waste of material.

Thanks to all that have commented so far. Im dead set on a colchester now, theres one in decent looking condition not to far from me. If I have to forget the cut knurling and go to form knurling for reliability then so be it, but would be nice to know exactly whats stopping the knurl from cutting.

 

[Beauvais]

Ref colchester....Perhaps have a look at a Harrison M300 instead?
A bit smaller and lighter, but quieter and probably more available in better condition, as a lot went into schools and colleges.
So you could find one at a good price that's hardly used, although a little abused....
Gap bead available too.

On paper they have everything I need, the 40" version that is. Will look into them!

 

[Mikel Levy]

Here are some pics of the setup. Briefly with the knurling, no matter what I do, it will not cut deep at all, It seems to form and not cut. The tool height I know is perfect, the angle is 2deg, I use coolant, it just seems to deflect when I try to plunge regardless of support or not. Ive tried changing the angle, the rpm, feed rate, same result everytime..

Look up the cut knurling instructions from Zeus and others. The initial setup for cut knurling is quite finicky. If you are cutting a knurl in the middle of a part, you will need to cut a groove in front of the knurled section at least as deep as the full knurl depth and chamfer the left edge of this groove, where the knurl will start. Your groove needs to be wide enough not to interfere with the cutter, so say about 1/4 inch or 6mm (just guessing). Position the forward cutting edge of the knurl wheel to be about 1mm to the left of the chamfer. Start the spindle rotating (but no z axis feed yet) and bring the cutter into contact with the work. Slowly plunge the cutter into the work at least 50% of the full knurl depth, or 100% of the full knurl depth if the material isn't too hard (aluminum, for instance). At this point the cutter is only displacing material, and not cutting, as there is no z axis movement yet. If you feel the force of plunging the tool into the work is becoming too great, slowly move the tool to the right onto the chamfer, at the same time plunging the tool in further. This move will reduce the amount of force required to plunge the tool to the required depth, but it's very important not to start the initial plunging on the chamfer itself, but slightly to the left of it, as described above. Once all this is accomplished, engage the z axis feed and start knurling, using plenty of coolant to wash away the swarf. If another pass is required, bring the tool up to the start of the knurl and slowly feed in the cross slide to pick up and track on the previously made partial knurl. Plunge the tool further into the work to the required depth, engage the z axis feed, etc. etc.

Here's a link to a brief video clip of me cut knurling on a piece of aluminum tubing. If you look closely you will see that after the initial plunge I move the cutter a little towards the tailstsock and then plunge the tool further to the full knurl depth (this is quite a coarse knurl--2mm pitch). Again, it's important to get a good initial plunge onto the diameter of the part. Anyway, the results speak for themselves. This was done on a Colchester Chipmaster lathe.
---Mike

 

[Beauvais]

@Mikel Levy
Thanks for the write up! Sorry for the delay in response, I will be trying knurling again very soon as i have just purchased a Colchester master 2500 and am in the process of giving it a deep clean and light refresh. The head sounded nice and smooth, not loud at all, it’s just not been properly cleaned in it’s time and I want to make sure everything is working as it should, for a lathe this age anyway.

 

[Beauvais]

Some progress so far..