bad finish milling wood

Good day

Please see photo

I used end mill 3mm for finishing

feed rate 25mm/sec
step over is 30%
spindle speed 8000 rpm
depth of the cut 8mm
stock thickness 18 mm


There are 2 issues as you can see in the photo

1-You can see the half circules (like if the bit is drilling holes not milling) along the neck line.
2-the second issue is the bit stroke lines like strips. I think this has to do with the spindle vertical alignment (Not sure because the alignment looks fine).


Philip

Thanks 

I would say that 8000 rpm is too slow with a 3mm bit I would double that.

Also is that MDF if so a lot of MDF is very woolly.

Clive wrote:

I would say that 8000 rpm is too slow with a 3mm bit I would double that.

Also is that MDF if so a lot of MDF is very woolly.

Yes

That is mdf

I have another machine running at 20k rpm, and I used mdf with almost perfect result but maybe something wrong with this lot of mdf. it looks weired. Or the finishing bit I used then maybe not this 3mm end cut. It has been a while I can not remember what bit I used for finishing with the last piece.

Regarding the rpm, I will have another shot with 24k. The roughing bit (5mm) smoke a lot of smoke at higher than 12k. I need to take the feed rate up to 35 mm/sec to minimize the smoke.




I will let you know in few days.

Philip

I pumped up the rpm to 24k. And I also used new finishing bit.

There is a noticiable improvment but the strips still there.

The only thing remain is the vertical alignment which will be very hard to fix as the machine has no adjustments.

This leaves me with no choice but to make new parts. Which is OK if the new parts solve the issue.

Philip

 

Is it possible to shim the spindle to get it aligned .  Pictures might help.

Raster 3-d relief milling is always going to have some ridge lines like that. It is the nature of the beast. Reducing the step over distance will make them smaller but they will never go away completely.

Clive wrote:

Is it possible to shim the spindle to get it aligned .  Pictures might help.

Good idea I should have thought of the shimming.

I mesured the alignment with carpenter square. Looks very good.

I will give one more try to reduce the step-over from 30% to 10%

If it still does not work, I will find a smaller diameter finishing tool (1.5mm) which I do not have now.

thanks

Philip

Todd wrote:

Raster 3-d relief milling is always going to have some ridge lines like that. It is the nature of the beast. Reducing the step over distance will make them smaller but they will never go away completely.

I almost arrived at this conclusion.

I highly appreciate your confirming this point. It makes me more confident now.


Philip

This type of milling is usually done with a small ball tipped tool, rather than a flat end mill. Using smaller step over with smaller tool diameters, is the only way to increase resolution. often making another pass at a different hatch angle can improve the finish.

Also the fuzzy and rough texture of MDF limits the quality possible. Often when MDF if the chosen medium, the only option to get a good finish is to have multiple steps of sanding and painting with high fill primer until the finish is acceptable. It is a lot of work especially with a detailed 3-d relief.

In my part of the world MDF and LDF does not look like that (US). I just looked at my LDF spoiler board which has relatively crisp tool marks. I have seen some sound proofing (?) panels that were extra fibrous. Try a different material. Urethane sign boards work great depending on density and type.