Milling a slot

[pgk pgkParticipant @pgkpgk17461]

I'm milling a series of 16mm wide 13mm deep slots across 70mm BMS with my chester superlux. I take 4 lots of 3mm deep cuts along the middle of the slot with a 12mm HSS rough cutter at 500rpm and finish the last 1mm. Then 1.5mm each side full depth then tidy up the last 0.5mm with a finishing cutter each side conventional milling.

I'm driving the cutter through with lots of hand sprayed coolant and keeping the chips just a shade towards golden. (I'm collecting bits to build a flood coolant system).

Driving the cutter like this on the first section of the slot and the differential forces each side of the slot/cutter and drag on the cutter mean that one has to slow the feed down markedly as one breaks out of the end of the slot. Of coures once the cenral section is cut out that stops being an issue.

Toms techniques recommends slotting with a series of overlapping plunges to almost full depth and then tidying up- claims that's easier on cutters.

I'm just wondering if there's other alternative ways that may be better…such as a thinner initial slot for chip clearance with a faster rpm/ feed speed and deeper cuts the full depth sides with 'medium cutters? Or whether blowing compressed air to clear chips is better than spraying coolant – not enough hands to do both until i build a system.

[pgk pgkParticipant @pgkpgk17461]

better ways?

[Ady1Participant @ady1]

On my more limited milling setup I started with 12mm full size and it took a while to finish because it was doing so much work, so I tried a 6mm and it zapped in to full depth, zipped up one side, across and down in a single pass, then a tidy up with the 12mm

Smaller cutters can sometimes be a lot faster and easier

[JasonBModerator @jasonb]

Try it with a 2-flute cutter as that won't get pulled over like your rougher which I assume is 4 flute

[pgk pgkParticipant @pgkpgk17461]

I had a go with 6mm… certainly ploughs OK full depth but I wasn't gentle enough towards the end of the slot and the cutter was destroyed on exit. It may be a way to go with a little more finesse but I only have one spare 5mm which needs reserving. I'll probbaly try in the future when i have some more.

I'll give it a go with a 2-flute. Of course it's not just the side pull there's a back drag as well. The rougher is 4 flute. I'm still getting a feel for chopping through a mini production run efficiently and cooking the tools and a balance between heavy cuts and machine vibration. The chester stand has too much flex too… with the mill on top you can manually twist the combo – I think it needs some reinforcing.

[mickParticipant @mick65121]

Might need buying a couple of cutters with modern cutting geometry . Take out the bulk using a ripper cutter, then finish the sides with a carbide cutter, both from APT on-line budget range, not expensive and last for ages. Orders placed before 4pm are next day by standard mail.

[BazyleParticipant @bazyle]

If snagging on breakout is a problem perhaps you can clamp on a sacrificial piece at the end. Slot drills get their name for a reason…..

Bound to be a nice big horizontal going cheap on ebay……

Edited By Bazyle on 11/11/2015 17:37:17

[pgk pgkParticipant @pgkpgk17461]

I dug out a 12mm 2-flute new endmill.. yes it avoids the side forces on breakout (thanks) but a much slower feed and more vibration. Perhaps on a wider slot a starting cut with a thinner 2 flute at higher rpm then take the sides…

APT have heaps of cutters.. any more specific recommendation and sizes? At the moment while I develop my feel for all this I'm a tad happier destroying the more economical cutters direct from china (I'm on the wrong PC to look up specifics but the site got a recommendationfrom from a member here).

I've got the hand feed feel for the way I've been doing it so on this bulk lot I'm half way through I'll probably carry on and then experiment later

[Tony Pratt 1Participant @tonypratt1]

I would use a 15mm diameter endmill [if you can go that big?] to rough out then swap to a sharp finishing cutter to size the slot.

Air or coolant is better than using nothing at all.

Tony

[MuzzerParticipant @muzzer]

You need to have the slide locks nipped up if you have any backlash (who doesn't?). When you are cutting the slot you have a lot of load on the leadscrew taking up the backlash but when coming out the end, it can catch (and it sounds as if it is). Try tightening them up just before you reach the end?

[JasonBModerator @jasonb]

Have a look at ARC for their premium HSS-Al cutter which work well and are not too badly piced in the larger sizes.

[Paul LousickParticipant @paullousick59116]

I just finished cutting a couple of 10mm wide x 25mm deep slots in stainless steel and had a similar problem with chattering. A 10mm cutter started to chatter when I was about 10mm deep. I used flood coolant at a slow speed but wore out a standard cutter when I got a bit deeper.

Got much better results by changed to an 8mm carbide cutter and taking a 1.5mm cut in one direction, moving the table 0.5mm sideways and cutting an overlapping slot on the return direction. Because I was only cutting on one side of the cutter there was no chatter. Then opened up the slot to the required width.

Edited By Paul Lousick on 11/11/2015 20:45:51

[pgk pgkParticipant @pgkpgk17461]

Lots of advice to take on board – thanks.

I've finished the batch of 16.5 x 13 slots and on to the 36mm x 10.2 deep mm slots. Again for expediency I've been using my 12mm rough cutter and taking care on exit of the first run of each layer then cut overlapping widths before going deeper. 2x 3mm deep runs and 2x 2mm deep then a finishing cutter for sides and base. A bigger cutter at slower rpm would cause more vibes..perhaps carbide speeds would help but the ones i used on a previous project were too brittle if they did catch. Because I'm knocking out a batch I've been trying to avoid cutter changes and pushing the feed rate with lots of hand spayed coolant. A one or two off would be a lot more relaxing..

Edited By pgk pgk on 11/11/2015 22:59:53

[doug nicholls 1Participant @dougnicholls1]

If I was using a 12 mm hss slot drill on a manual,I would make sure my cutter is nice and tight in the collet,I would run at 400-450 rpm,up cut it at a 12mm depth cut,full lock on y or x depending on which way you're feeding and a light lock on the way you feed, feed it in by hand, coolant in fairy liquid bottle, have about 15 of them near hand,squirt it so the chips are clearing.

Piece being clamped at the end is a good idea if practical

When milling the 1.5 on the sides(I would take off 1,8mm leaving .2 on sides for finisher), go down 12.8mm leaving .2 on depth for finisher.

2 or 3 mm depth cuts are too small for hss cutter over 5mm diameter , you're wearing the bottom and not utilising the sharpness of the sides

[Author]

Posts