??? straight or twist

[bman]

hey guys which is better for plowing groves with a router a straight bit or a spiral up cut already have my beginning and ending pilot holes looking for the smoothest sides this is in MDF (i would think the spiral )

barry

[Ray Martin]

Barry,

This is another topic that can bring about some discussion. An up spiral pulls debris out of the groove more easily and makes for clean cuts with less chance of heating up / burning. The surface, however is unsupported so you could have some tear-out or chipping. Eliminating that tear-out is the purpose of a down spiral.

You could score the edges of the groove or dado and that would probably eliminate the tear-out.

Ray

[Nativespec]

I use a spiral down cut. The down cut prevents damage to the surface since it is pulling down on the fibers. Up cut bits are for slots that will show on your surface (pulls the fibers up as it cuts). Straight bits are for the recycling bin.

David

[bman]

in this case i will be cutting from the bottom to the top MDF core to a laminate top
and David..... love that "straight bits belong in the recycle bin"
the exit point on the top is the most important so i guess i need to stick with the up cut

[DavidF]

If the mortise is deep then an upspiral might reduce heat and clogging, but will leave a nasty top edge, not a problem for a mortise and tenon with a shoulder, but no good for an exposed top groove. In MDF, with a shallow groove it probably doesn't matter too much either way; straight or down spiral, but not an up cut bit. Generally I am changing to spiral bits because of the lower tendancy to pull out the grain while template cutting curves especially in end grain - bottom line, if you're going to buy a new bit for this job then make it a down cut.

[DavidF]

Originally Posted by bman

in this case i will be cutting from the bottom to the top MDF core to a laminate top
and David..... love that "straight bits belong in the recycle bin"
the exit point on the top is the most important so i guess i need to stick with the up cut

Ah, if you're cutting all they way through from the bottom to the top then yes, an upcut is the way to go.

[bman]

down cut it will be ...... what about a compression bit anyone every use one of those?????

[DavidF]

Originally Posted by bman

down cut it will be ......

Do you mean that??? I thought we all decided on an up cut

Never tried one of those - always too expensive..

[bman]

well is't going to be a straight bit the Ral woodcraft didnt have either up or down they say the down cut arent very popular didn't want a HSS bit (allready burned one of those up ) MDF is tough on HSS bits should order on line last sunday .....so i have add another 2 WS bits to the collection got the shaker bit too @15 $ off can't beat that plus getting 3 bearings ..... all in all a good day ..ready for the weekend

Barry

[DavidF]

If you are buying bits I would highly recommend MLCS. Good quality, quick delivery AND FREE SHIPPING!

[Nativespec]

I find the downcut more popular in my work. I have both the MCLS and CMT-I got the CMT from Amazon for about 1/2 of what Woodcraft sells them for.

David

[jonnyfontaine]

i've actually always had good results with a regular old straight bit when cutting MDF actually MDF is one of the few times i feel i don't need a spiral bit and one of the only times i think a straight bit works really well... in my opinion i would think that a straight bit would suffice and use a spiral bit for a wood that would give more trouble for a straight bit... that's just my opinion though

[bman]

Johnny i would agree ...i think a lot depend on the quality of bit ...... mine are ebay specials carbide but cheep i have had them about 3yrs now use um twice maybe 3 times and toss them been replacing with the CMT and W\S BIG!!!!! Difference i got a down cut CMT on the way from amazon

Barry

[McRabbet]

Two years ago, I broke a 3/8" x 1-1/4" x 3" downcut solid carbide CMT spiral bit while cutting 1" deep mortises for some porch railings in PT SYP (I hit a knot) and the company (Sommerfield Tools) replaced it without any hassles -- they are superb bits and guaranteed not to break.