How to avoid splintering in plywood?

[ilsaarin]

Hello

I made one clock out of plywood and got a lot of splintering. Top veneer splintered a lot. I use 6mm single cut end mill. What kind of mill, rpm and feed speed you guys are using when you are pocketing or cutting out parts from plywood? Or do you have any other tricks? Taping the surface first?

Ilkka

[tmerrill]

Ilkka,

Biggest tip I can give you with plywood and protecting the top veneer is to use a downspiral bit. It will shear down on the veneer and give you a nice clean cut.

If you are cutting completely through the plywood and need to protect both top and bottom veneer layers, then look at a compression bit. They will have a downspiral at the top of the bit and an upspiral at the bottom.

Tim

[ilsaarin]

....Just ordering down spiral mill....

Thank for the tip. I would never figured this out by myself.

Ilkka

[ckurak]

Ilkka,

I agree with Tim on the two types of bits he mentions and for the same reasons.

A few words of caution on the compression bit may be helpful if/when you get one. If you are doing multiple passes to make your cuts, be sure that the first pass is deep enough. Look at the end of the compression bit. Typically the up-spiral section is about a quarter-inch or so. When the bit is cutting with that quarter-inch, it is pushing the chips upward. If your first pass is only 1/8" deep, then you will see LOTS of chipping and splintering on the top veneer of your plywood. Subsequent passes (they will be deeper, of course) will not push the splinters back in place.

Likewise, if you try to cut through too deeply (say more than 1/4" into your spoilboard), then the downward spiral will make a mess out of the bottom veneer. This case is not too likely, as very few of us would attempt to cut that deeply into the spoilboard. Well, at least not on purpose.

So, multiple passes are perfectly fine with a compression bit, just be sure to get the first and last passes correct. A test run will tell you immediately if you have it right or wrong.

[ilsaarin]

Hello

and thanks for advice. Term "compression bit" is new to me, so I had to find out what kind of bit it is. I found this: http://www.toolstoday.com/p-5638-cnc-co ... flute.aspx

Is this the bit you meant?

Ilkka

[ckurak]

Ilkka,

Yes, they are the compression bits I mentioned. Notice the B1 dimension in their diagram. That is the length of the up-spiral. So, if your first pass isn't greater than this dimension, you will get splintering of the top edge. Likewise, if your last pass is deeper than this dimension (plus the thickness of the wood), you will get splintering of the bottom edge.

In my shop I use compression bits for plywood, laminated veneer, and melamine. Each of these is subject to chip-out and splintering. A good, sharp compression bit will prevent this damage.

Also, many different companies make compression bits at a number of different price points.

[rrrevels]

Just a note of caution concerning down spiral and compression bits on the CNC machine. There have been several posts made on other forums concerning use of these types of bits where enough heat has been generated to start a fire in the spoil board. Be very aware while cutting. Watch for embers and smoke. One of the above mentioned posts was using a vacuum hold down and didn't notice the smoke until the damage to the spoil board and project material was quite severe. I believe it is like most everything else concerning cnc, stay focused and watch and listen. Most of the time problems will announce themselves.

Russ

[ilsaarin]

Can you give me some tips about the companies who sells these bits in the web? Small ones (less than 8mm diameter) seems to be hard to find where I live.

Ilkka

[ckurak]

Here are three that I use.

http://www.centuriontools.com/

https://www.onsrud.com/

http://www.magnate.net/