Warco VMC spindle knocking

When milling with a 40mm 3 insert cutter today on 19mm alumiminum alloy. I noticed a distinct knocking from my VMC spindle. On investigation I find that if I grip the spindle pulley and the lower spindle. I can detect some radial slop/backlash. At 20 mm radius, I get about 0.18mm of movement, which works out at about half a degree if my school trig holds up I guess that this can only come from the location of the splines in the spindle. It doesn't seem to vary with quill position. There is no detectable runout on the spindle itself, so it is not impacting finish or accuracy.

I have never really noticed it before (not that the insert cutter has had much use). I conclude that the intermittent nature of of the larger endmill is amplifying the noise as each insert engages/disengeages with the work. The machine hasn't done a huge amount of work, I have had it from new and has only been used on light ME tasks.

Is this anything I should be concerned about?

Hi Stuart,

Have you locked the quill and applied the cut by using the table?

Hi, yes, quill is locked and teh cut is via is via X axis on the table.

It is common in a machine with a splined drive between pulley and spindle:

https://bbs.homeshopmachinist.net/forum/general/70742-bridgeport-rattle-in-head-when-taking-heavy-cuts

https://www.practicalmachinist.com/forum/threads/rotational-play-in-bport-spindle-belt-drive.245080/

http://chaski.org/homemachinist/viewtopic.php?t=87545

https://www.model-engineer.co.uk/forums/postings.asp?th=123926&p=6

Solution is to bias the spindle against the pulley spline so the backalsh is always taken up and cannot come into play when a cutter tooth exits the work.

Have a look at HPC's catalogue for anti-backlash gears. In principle, you need the same thing.

The solution above, in the Beaver thread stops operation of the quill.

I cannot find it now, but there is a photo on Practical Machinist somewhere showing an internally-splined collar that goes over the spindle, with some springs connecting it to the drive pulley. The spring pressure pulls the splines into contact at all times. This arrangement allows the quill to be used.

Hi

I have the same problem when using a large cutter on my VMC.- any other mill is likely to exhibit the same problem to a greater or lesser degree. The basic cause is down to the size of cutter vs material width.

Assuming that the aluminium is 19mm wide, with a 40mm diameter cutter (3 teeth) you have an interrupted cut for much of the cutter's rotation due to the lack of teeth in contact with the workpiece. This is a particular problem if the cutter is on the centre line of the workpiece.. Exactly the same situation as the 'knocking' of an interrupted cut on the lathe.

Moving the cutter so that the tooth just skims to edge of the material should improve the situation, although it probably won't eliminate it altogether. An alternative would be to use a cutter with more teeth, such as a shell mill.

Good luck - please let us know how you get on.

Thanks for the feedback, some very good points

Hi Roger,
Back on the mill today and you were spot on. Moving the cutter to one side instead of straddling the work has dramatically reduced the noise. Thanks for the tip.

Hi Stuart

Pleased that you've seen an improvement. Thanks for letting us know.

I'm also experiencing this issue! I contemplated fitting a few 0.2mm shims either side of the two spindle parts to try and reduce this however sticking them in place is proving pretty difficult. Can you explain in more detail what you mean by moving the cutter to one side.

Thanks

Simon

Simon, see Roger's post above for a good explanation, the idea is that you are trying to minimise the interrupted cut and smooth the entry of the tooth. If the cutter is larger than the workpiece you are running the cutter down the centreline. The tooth entrypoint will be at 90 degress to the edge of the work with quite a high impact. Moving the cutter off to one side so it just clears the edge of the work will result in a much shallower entry point angle for the tooth.

Hi Simon

Ideally, you should have teeth in contact with the workpiece at all times. if you can eliminate the interrupted cut altogether, then it's far kinder to the machine and to your cutter - the surface finish will almost certainly be better as well.

I have a good quality inserted tooth cutter - 50mm dia with 3 teeth - that I hardly use due to this problem.

As Stuart says, the entry angle is also reduced dramatically which will reduce the knocking - reducing the feed rate should also help. Give it a try - an old machinists trick that really works.

Good luck.

Stuart, are you sure it's not the drawbar vibrating, it vibrates on mine if I'm using a large face mill (50mm)

Mark P.

My VMC knocked quite badly when I first got it. Traced the problem to the motor pulley. I slackened both pulley grub screws and then tightened the one opposite the key as tight as I could, then tightened the key side screw just snugly. Cured the knock.

I see that makes sense! I'll ditch the shims and put it all back together. If that's how it is then that's okay I just wasn't sure if this was normal! I'll do some experimenting with cutters and points of entry. Many thanks