Spoilboard surfacing - strange problem/result

[Nealieboyee]

Hi All,
I just finished squaring and making parallel etc my machine (again) and went to surface my UHMW/HDPE spoilboard. Have a look at the photo. I only took off 0.5mm using an 8mm 3-flute carbide endmill. This plastic tends to come off as a layer rather than being cut, when you're taking off so little, however my problem is certain areas of the spoilboard are absolutely perfect. Can't feel any undulations. But other areas are weird. After taking off the hairy bits left over with a chisel, its better, but still not nearly as smooth as other areas.

Any idea why this would be happening?

https://live.staticflickr.com/65535/47673460022_1f959a711e_k.jpg

[magicniner]

I'd guess it's as a result of the fog/steam in your workshop.

[Nealieboyee]

I'd guess it's as a result of the fog/steam in your workshop.

No but definitely the glare from the floodlight. Apologies, it was the best I could do at the time.

[magicniner]

Carbide endmill on plastic screams problems unless you have a particularly sharp edge, try a high speed steel cutter with a very sharp edge.

[Nealieboyee]

Carbide endmill on plastic screams problems unless you have a particularly sharp edge, try a high speed steel cutter with a very sharp edge.

Ahh so that's why it was pushing the plastic instead of cutting. Very thin cut too so that wouldn't help.
I don't have any hss bits yet but I'll put a wooden board in top of the plastic and surface that with the carbide bit and see the results. Just trying to check everything is square and true.

Thanks very much

[Lee Roberts]

Could give a single flute cutter a try as well, plastic melts when it gets hot, the less chip re-cutting the better, although that counts when your cutting deeper into the material i.e pockets and stuff like that it could help here to,.

Keep an eye on your chip loads as well, when they get to low you start to see rubbing rather than cutting.

[Voicecoil]

Hi Neal - have you managed to skim this spoilboard before with better results?

[Nealieboyee]

Hi Neal - have you managed to skim this spoilboard before with better results?
This was the first time with this spoilboard. Why do you ask?

Something else is wrong though. I have a feeling my x axis rails are bowed. I need to adjust them tonight. The cut is perfect on the left but not in the middle. Better on the right. That tells me the spindle isn't moving in a straight line and is climbing towards the middle of the gantry.

[Voicecoil]

Because if you hadn't had a good skimming before I was going to suggest a very similar prognosis to the one you've just come up with! Though it might be more than a matter of the rails being bowed - obviously they're less stiff in the middle than at the edges, so the spindle can move about more.

[Lee Roberts]

Personally I thought at first that the spindle wasn't quite perpendicular to the bed and needs minute adjustment. It looks to be spot on when going in what ever the directions are to the left and right of the pic (top to bottom of pic), whereas you can see tiny lines/ridges on the cuts that go from left to right of the pic (the problem areas).

[Nealieboyee]

Could give a single flute cutter a try as well, plastic melts when it gets hot, the less chip re-cutting the better, although that counts when your cutting deeper into the material i.e pockets and stuff like that it could help here to,.

Keep an eye on your chip loads as well, when they get to low you start to see rubbing rather than cutting.
Correct! I had a look at the feathered strips that came off the material, and they were kind of stuck together.


Because if you hadn't had a good skimming before I was going to suggest a very similar prognosis to the one you've just come up with! Though it might be more than a matter of the rails being bowed - obviously they're less stiff in the middle than at the edges, so the spindle can move about more.
Thankfully, the rails weren't bowed. It was the plastic cut that was throwing me off. The bad areas must have been where the plastic was melting or something. I added a piece of wood on top and surfaced that. Much much better.




Personally I thought at first that the spindle wasn't quite perpendicular to the bed and needs minute adjustment. It looks to be spot on when going in what ever the directions are to the left and right of the pic (top to bottom of pic), whereas you can see tiny lines/ridges on the cuts that go from left to right of the pic (the problem areas).
Correct again. My left to right adjustment during tramming was off. Its spot on now. The front to back (tilt) needs a 0.1mm shim, but i've got it really close. I can see the vertical lines in wood, but hardly feel them. I can't see horizontal lines at all.

Only problem now is my gantry still isn't perpendicular to my y axis, so cutting a rectangle of 50.1mm x 40.1mm gives me a diagonal of 63.8mm instead of 64.2 mm. However, both diagonals are identical.....weird