[ruffle]

Being very much a newbie, could I ask for folks opinion on whats causing this effect?

Attachment 229682

The part is triangular and the other two sides and inner cuts don't show the same problem:

Attachment 229684

It's 12mm thick 6082 aluminium, 6mm 2 flute HSS cutter, profiled at 1.5m DOC, 2500rpm, 240mm/min then a cleanup pass of 0.04mm at full depth and 750 mm/min. WMD30LV mill.

The side showing the marks was on the left and my air nozzle is on the right of the head.

Attachment 229686

This makes me think it's recutting chips but before I rush off and 'do something' I thought I'd ask if the marks suggest something else.

[hjl4]

From what I can see, some chatter, but lack of coolant is the problem. Slow feed speed and rubbing basically, causing melting of the stock. This is where flood or mist coolant works wonder. Did you use WD40? It would of minimized that also.

[Superman]

The bottom pic has me worried
- the vice is holding the stock, jaw pressure would collapse the stock closer into the cut and the part would tend to move toward the rear ( moving front jaw )
making the part NOT do a clean-up along the front edge.

my suggestion
- clamp the stock so that there is still material inline ( both sides ) from rear to front jaws after machining.
---- Or not use a vice at all. clamp a waste plate onto the table, clamp the stock onto the plate, machine inner details, insert screw to secure part (D&Tap a hole in waste plate), machine outer edges ( you need to support the actual part you need to keep )

PS
your cut speed for HSS is only 47 m/min, lift it to 60m/min ( say S3183 )
rough feed is 0.048mm per tooth ( could be faster, say 0.1-0.15/tooth ) ( F800.)
finish feed is 0.15 per tooth ( I'd leave 0.1-0.2mm on for finishing & go a little slower, let the cutter bite into material instead of rubbing )(F500.)
I'd use a little bit of coolant with the air ( to stop the chip buildup on the cutter ( try a little WD40, or kero )

[ruffle]

Thanks for the comments chaps.

The profile wasn't meant to break out of the stock on the left hand side.... I forgot the tool width when setting X to zero

I'll try again with a) some WD40 b) more stock on each side to support the job c) paying attention to the chip clearance and d) a bit deeper and slower cleanup pass.

The marks were only on the left hand face so it's surely got to be either lack of chip clearance or the stock vibrating and causing chatter.

I'd like to run the spindle a bit faster but 2500 rpm is about the max. In fact the mill is only meant to go to 2300 but mine will run a bit faster than that (2900 according to the Mill's display but 2500 according to my tacho).

[Superman]

The marks were only on the left hand face so it's surely got to be either lack of chip clearance or the stock vibrating and causing chatter.

I'd like to run the spindle a bit faster but 2500 rpm is about the max. In fact the mill is only meant to go to 2300 but mine will run a bit faster than that (2900 according to the Mill's display but 2500 according to my tacho).

If this is the case, then it is caused by the chips not being cleared away from the cut line, a faster RPM would tend to lift the chips out of the groove, and the liquid ( WD40, kero, air+coolant ) helps by lubricating the cutting edge, making chips release quicker. You also do not want the material to heat up & stick, otherwise it will end up being a 10mm aluminium bar pretending to be a cutter.

The air nozzle needs to be closer to the collet nut, pointing more downward ( to blow around the cutting edge ), ( or a setup of nozzles around the holder )
- you may wish to invest in a smaller collet system for the smaller cutters ie ER16 with straight shank to fit into an ER32 holder - so that the air blow can get closer to the cutting area

I suggest trying to make some sort of venturi type air blow system that sucks from a liquid pot ( thru a small tube, with a inline tap, to regulate flow that joins onto the air line by a Tee piece - air blows across the top of the Tee to create the vacuum )

[Fastest1]

Spindle speed is not always your friend. It has to be matched with feed. In fact try to do some tests at slower spindle speeds or faster feeds.

[AVRnj]

I get that from time to time as well.

Recently I have been working on my Y axis bearing block, and I am making 2 of them in case I mess something up.

I wanted to have nice rounded corners so I profiled the final size out of a bigger 38.1mm block of aluminum.

The first one had a lot of those marks on it, all I did was try to blow the chips out with air.

Second one I used the exact same clamping system (to the table through a center hole) and exact same feeds and speeds, same cutter. This time every few depth drops I hit it with some wd40 and I did not get one of those marks.

I know it is not that simple and I would much rather be able to cut without having to apply wd40 so often, and as others have mentioned I would think spindle RPM combined with feed speed can probably contribute, I am still trying to get the hang of all this as well.

[Fastest1]

This could also be from backlash possibly. Maybe 2 sides were cut in the direction the backlash had already been taken up. The other side done right on the change and the backlash was still there. Just a thought.

I will tell you this, in my experience (and I am just a hobbyist) it is hard to get good finishes in the beginning. It will take a while to commit to a proper feed and speed. Beginners tend to default to higher spindle speeds and or lower feed rates. Neither of those ideas helps finish or accuracy. Really just shorten tool life, lengthen job time and work harden the stock making it harder to cut. try to cut many things first, scrap whatever you can find. Fluctuate between climb and conventional cuts to see the results for yourself. Set up and stock prep are everything.

The people who do this for a living and maintain tight tolerances on piece after piece, all day long are professionals. There is no doubt about it. Many moving targets to focus on constantly. Keep up the enthusiasm.

[LongRat]

I'm convinced the problem is the breakout of the cutter from the stock on the left side, causing resultant poor support of the work piece for the clean-up pass. I would bet money that the finish in the area concerned was better before the finishing skim pass.
I also agree that the finishing pass is too fast and shallow. I usually leave 0.2mm on and skim off at about 250mm/min in this situation. I would also double the thickness of your holding tabs.
I don't think this has been caused by backlash - that would also affect the position of the roughing passes and not leave you with an asymmetric surface finish issue. BTW I also run a WMD30LV. Do yourself a favour and upgrade to a belt drive on the spindle, 4-5000 RPM. This makes a world of difference to the mill.