MDF Edge Quality

[beacon14]

For my own and anyone else's future reference I thought I'd post a couple of pics of the edge quality we are seeing on 1/2" MDF. These cuts were made using a 2 flute carbide spiral downcut bit from Onsrud, these are the bits that were purchased on eBay from their overstock outlet. Machine specs are below in my signature.

These were cut with two passes, both conventional direction, the first leaving an onion skin of .02", with spindle speed of 8400 RPM and move speed of 1.5 ips. 2nd pass cuts through the onion skin at 2 ips. The nature of this project requires us to cut on the line, so no allowance is used between cuts - both cuts follow the same line. (The onion skin is to preserve the vacuum until all the waste is roughed out, if not for that I would make the cut in a single pass).

In the picture you can just make out where the onion skin left what appears to be a slight ridge (the two pieces on top are upside down, so the 'ridge' appears on the top). In reality I had to take another look at the parts after I saw the pictures - the ridge is barely discernible to the eye and can't be felt - the pictures seem to show it more prominently than it shows in real life.

Most of our cutting is done at much faster speeds than these, but for this customer edge quality is more important than speed. We are happy with these results. I'd be curious to see what others are getting as far as edge quality in MDF.

[steve_g]

David

Nice Cuts! I'd say just slightly better than I'm getting with my 3:1 belt drives on my PRT Alpha.

What diameter is the bit you're using?

SG

[adrianm]

Looks similar to the finish I get on my PRS Alpha with the 2.2 spindle.

I use 6.35mm 2 flute down spirals at 6.5/2.0 ips @ 14k rpm with 7mm pass depth.

MDF can vary a lot though. I had a batch a while ago that wouldn't cut cleanly at all at those speeds.

Whenever I get a new batch in (I buy 100 sheets a time) I run a series of test cuts before doing any customer work.

[Brett1970]

i get that little step over look when i cut it too. I use a compression spiral to cut all mine. With the compression bit, it packs the dust in the cut pretty tight, i don't have an issue with parts moving around at all when cutting all the way through.

[beacon14]

Sorry, meant to say 1/4" 2-flute down cut. We mostly use 1/4" compression bits (and mostly cut 2-sided melamine) but this client's projects have a lot of pockets and small holes so we use the downcut bit and a nice clean spoilboard. Also machine was upgraded to 7.2-1 geared motors on x and y - forgot to put that in my signature!

I know what you mean about the varying properties of MDF. We see that with melamine as well.

[jTr]

David,
Just cut a stack of 10 sheets of MDF core red oak ply - photos show results using a plain old Whiteside 2 flute .250" straight bit.

Why no spirals?
Rabbets and Dados are part of routine. Like you, I've found compound spirals tear veneer since the first .25" of the bit is upcut - especially on end grain, which is typically where those dados are cut. I frequently use down-cutters as well, but this seemed a great opportunity to show that a standard straight bit can do quite nicely.

Note ruler in photo - those ripples are about .010" wide. At a glance from a foot or two away, they look perfectly smooth. No ridge or step present from final pass, as I do 3 passes in climb cut to .060". Final .015" is cut through with a "conventional" counter-clockwise cut. All passes are 4 ips @ 12,000 rpm.

Sometimes you can actually see with the naked eye as you watch that last "hair" of dimension being shaved off on the final pass, eliminating the wider swath left using the climb cuts. When using a downcut spiral, a similar set of micro-"tracks" can appear - they are simply angled rather than perpendicular like these.

I am thrilled with this quality - try to beat that shoving a sheet of ply across the tablesaw! Lifting pieces of super-clean cut plys off the bed that include exacting dados, rabbets and shelf pin holes is truely wonderful.

Love my 'Bot!!!!

Jeff

[beacon14]

Hmm, nice edges. I rarely think of using the straight bits except for in a router table but with the mortises etc. the compression cutter is not ideal. The fragile veneer on the bottom face makes it hard to get a good cut with the down spiral unless you resurface the spoilboard after each sheet. The trade off is more passes so longer machining time.

Without thinking of a straight bit I might have ended up using a down spiral for the joinery and then switching to a compression cutter for the through cuts. Less machine time and optimized cutting but the operator's time to change bits figures in. O to have a tool changer.

[kubotaman]

David's comments in regards to cutting thru with a downward spiral bit brings up a question. I have wondered why a person could not cut with the same downward bit but on the bottom apply masking tape to stop the "ripping" of veneer on the bottom. I admit it may be time consuming but I do think it is doable. Just a thought. Not economical for sheets but on small projects it would work. Just a thought.