Up or down Spiral.

jj777746 said:

I have never used a spiral bit but want to purchase 2 of in the near future. I noticed Infinity Cutting Tools advertising a set of 2 upcuts especially for using on plywood but was wondering if upcuts are suitable for rt use.I know this was discussed previously but I can't find it.,Much obliged for any assistance. Jamesjj777746

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they certainly are James...

In an RT, the up cut pulls the dust/debris down towards the motor. Good dust collection will help prevent the dust from fouling the motor. JMO but, I prefer the down cut for that reason. And, I have excellent dust collection. Seeing the amount of dust and chips collected pretty much confirms my choice.

Also, an upcut spiral will chip a lot when cutting dadoes and rabbets in plywood. Downcut will give a much better edge.

Spiral bits will cut one of the edges real well and the opposite edge may have some tear out. For example, an upcut spiral mounted in a table router will leave a clean cut on the top face but likely some tear out on the bottom face. Opposite effect with a downcut spiral. The up and down orientation is referenced by the router not in the table...

A "compression" bit cuts both faces because the bottom of the bit cuts up will the rest of the bit cuts down (from the wood's perspective)...they are available with and without bearings, top and bottom.

Example only... https://www.amazon.com/Whiteside-Router-Bits-UD2102-Compression/dp/B0012K5YDK

If you plan on cutting a lot of plywood you will eventually need to resharpen or replace the bit.
Whiteside will resharpen their bits for free (plus postage)
Infinity does not.
For that matter, I can't think of anyone who does.

The only time I used a spiral bit was making sink cut-out in vanities,and I don't remember which it was up or down. All my bits are straight and I am happy with them.
Herb

Thanks for the outstanding responses. I also meant to ask How the heck do you sharpen a spiral Bit? James

jj777746 said:

How the heck do you sharpen a spiral Bit? James

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Beats the crap out of me, but Whiteside does it.
MAYBE put it back on the machine that ground the bit to begin with, but tighten the tolerances a bit??

All I know is that it works.

smitty

Yes, they are sharpened on the same machines that make them.

I'd be surprised if Whiteside sharpened spirals for free. We usually pay about $20-$25 to have 1/2" spiral bits sharpened. Sharpening a spiral bit is not a fast process, and the grinders can cost $500,000.

And when they get sharpened, they get considerably smaller, depending on how worn they are. The bits we get sharpened usually end up about .015-.02" smaller with each sharpening.

ger21 said:

Yes, they are sharpened on the same machines that make them.

I'd be surprised if Whiteside sharpened spirals for free. We usually pay about $20-$25 to have 1/2" spiral bits sharpened. Sharpening a spiral bit is not a fast process, and the grinders can cost $500,000.

And when they get sharpened, they get considerably smaller, depending on how worn they are. The bits we get sharpened usually end up about .015-.02" smaller with each sharpening.

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That was my thinking too ,but it does not make them more inefficient than before. They run from 1/8"-$22., to 1/2"-$93 new, so it wouldn't pay to resharpen the smaller ones, when shipping is included, IMO.
Herb

ger21 said:

I'd be surprised if Whiteside sharpened spirals for free. .

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FWIW I sent in a spiral bit to them about this time last year.
Cost was $7.50 to remove & remount bearing ( as opposed to R&R) to allow them to sharpen the bit. And return postage. Turn around was a week, IIRC.

I didn't check diameters before & after but the diameters looked close to each other (eyeballed).

And yes I was surprised also that it was free. Maybe they like me???

Afterthought---Maybe they were gracious b/c they felt sorry for me? The bit when I bot it was close to $100.00 back about 15-20 yrs ago