bad finish milling wood

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21 Dec 2021 09:15 - 21 Dec 2021 09:22 #229615 by PhilipME
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 
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Last edit: 21 Dec 2021 09:22 by PhilipME.

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21 Dec 2021 10:30 #229618 by Clive S
Replied by Clive S on topic bad finish milling wood
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.
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21 Dec 2021 10:55 - 21 Dec 2021 10:59 #229619 by PhilipME
Replied by PhilipME on topic bad finish milling wood

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
Last edit: 21 Dec 2021 10:59 by PhilipME.

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22 Dec 2021 08:52 - 22 Dec 2021 08:53 #229707 by PhilipME
Replied by PhilipME on topic bad finish milling wood
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

 
Last edit: 22 Dec 2021 08:53 by PhilipME.

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22 Dec 2021 09:23 #229708 by Clive S
Replied by Clive S on topic bad finish milling wood
Is it possible to shim the spindle to get it aligned .  Pictures might help.
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22 Dec 2021 14:54 #229732 by Todd Zuercher
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.
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22 Dec 2021 15:11 #229734 by PhilipME
Replied by PhilipME on topic bad finish milling wood

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

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22 Dec 2021 15:15 #229735 by PhilipME
Replied by PhilipME on topic bad finish milling wood

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

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22 Dec 2021 15:39 #229742 by Todd Zuercher
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.
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22 Dec 2021 16:04 #229743 by OT-CNC
Replied by OT-CNC on topic bad finish milling wood
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.
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