Spiral Router Bits?

[JayStPeter]

I finished making the ShopNotes mortising jig this week. I would like to use spiral router bits with it. I think the first order of business will be a 1/4" spiral upcut bit.
My question is going to be on brand and technique. I've bought two of these exact bits in the past, one MLCS and one Freud. Both broke after less than 10" making a 1/8" deep cut. I figured the MLCS broke because of the brand. But, the Freud wasn't cheap. In both cases I was making stopped drawer bottom slots on my router table. Neither bit actually made it more than part way through one drawer part. My plan was to do two passes to get the 1/4" depth I desired. I finished both sets of drawers with a standard two flute straight bit and used one pass for the full depth. Brand, technique, or wrong application?

Thanks,
Jay

[Steve Clardy]

Spirals don't seem to last long. Lots of pressure on the end of the bit.
I have a 7hp overhead pin router that eats bits for breakfast.
I've used regular steel ones and full carbide ones. The solid carbide ones seem to break quicker.
Never tried Onsrud bits. They are supposed to be pretty good from what I hear.

[Greg Mann]

This should be child's play for a good spiral upcut which is, essentially, an end mill. We routinely mill 1/8 deep in steel and aluminum with 1/4 inch bits, although admittedly not at the feedrates one would expect in wood. I have never heard a bad word about Onsrud, and a cutter that doesn't beark is cheaper than one that does. Give yourself the best chance of success.

Greg

[Alan Turner]

I have used MLCS spiral bits, including the 1/4", for years, and have never broken one ever. I wonder if your feed rate is at issue. I use them because they are inexpensive, and have free shipping, and have no complaints. But, for my slot mortiser, I do not use them, opting instead for Bentz Tooling end mills, solid caribde. And, I have never broken one of these either. You might consider playing with your feed rate. A 1/8" cut is not likely to be the problem.

[Andy Hoyt]

I do tons of slot mortising with an Onsrud 5/32" double flute solid carbide sprial upcut in a milling machine running at abot 2500 RPM. I cut about 1/4" deep at a time using a cross vise. I can move the vice just as fast as I want. Never had a bit break, but sure have dulled them after a few mile's worth of use. Doesn't seem to matter if I'm milling pine, maple, or whatever. Send me a PM if you need numbers or contact info.

[JayStPeter]

Onsrud is at the top of my list of potential sources.

The feed rate of the first bit is definitely suspect. It was when I first started WWing. The Freud was just a few months ago. I specifically fed it slow fearing that I would break the bit.

Jay

[Ian Barley]

I don't use spirals anymore because they break too easy and cost too much to sharpen and, in my application - gave no particular advantage. I use an Onsrud inverted pin router and have used Onsrud bits - the bits are probably the best that I have used but they still break and they still cost 6-7 times as much to sharpen as straights and 3-4 times as much to buy.

I can see that spirals might work great at a milling speed of 2,500rpm but they are , in my experience, of no greater value at a routing speed of 20,000rpm

[Norman Hitt]

One other thing to consider, Jay, is that to "lessen the SIDE stress" on the upcut spiral bit, try to use one with the Shortest "Cutting Length", that you can use, but be sure that the spiral cutting part is longer than the depth of the mortise you intend to cut so it will clear the chips from the mortise slot. A bit with NO MORE than 1 inch of "cutting length" would be fine for a 1/4" deep mortise. In other words, the longer the cutting length of the bit, the easier they are to break, and will require a slower feed rate than one with a shorter cutting length, (the fulcrum effect, I call it), (in Aircraft design, it would be called "Wing Bending Moment"). :D .

[Mark Singer]

I am using a Whiteside 1/2" x 4'' upcutspiral on the doors I am making...I have cut over 100 mortises so far , each is 2 1/2" deep and the bit looks new. Make sure the chips have a way to escape and are not covered by the jig. Slow the router speed down....about 5000 to 8000 rpm is good for a 1/4" bit....make small bites each time. Osrund is another very good brand. I have the same 1/4" spirals for years! I made over 160 mortises for 10 chairs with the same 1/4" bit! A spiral should not be used with a template giude bushing....it acts like a roof and does not let the chips evacuate....If you guide the routr base with the jig instead of the template bushing , you will eliminate the problem. Check out this post:
http://www.sawmillcreek.org/showthread.php?t=22781&page=2&pp=15&highlight=balboa

Scroll down..."Better Jigs for Better Routing"

[Ralph Barhorst]

I have used 1/4" end-mills for several years. I buy them at the big auction site and they are much cheaper than spiral router bits and work just as well if not better. I have only broken one and it was my fault. You should buy the two flute design to allow the wood chips to flow out better but the 4 flute also works well and would probably hold up better than the two flute. Just make sure that the length is correct and the shank is also 1/4".

[Leo Hill]

Seems to me that some tooling that is great for metal machining would work just fine for wood machining. Try MSC for lots of [relatively] inexpensive tools and tooling. http://www1.mscdirect.com

Leo

[JayStPeter]

Thanks for the ideas guys. I will purchase an Onsrud 1/4" bit with an upcoming LV order.

Mark, I specifically chose the Shopnotes jig shown for its ability to clear chips. I wanted the OF1400 dust collection to be able to collect on whatever jig I made. That immediately eliminated many of them since they were template guide based. The thing I have since realized is that I'd like to use a 1/4" bit for the 3/4" wide mortices I am getting ready to make. Template guide based would give me that flexibility. Fortunately with this jig, I just need to make a new top plate and I can go that direction if I want to.

Jay

[John Lucas]

Jay,
Several times there has been mention of how poor 1/4" spiral bits are in handling cross stress...I agree. I use up spiral bits a bit differently. I plunge all the way at the two ends of the mortise and then in between trying to "drill" complete holes. When done, I move laterally between the "holes". This makes a good mortise and is easier on the up spiral bit.
I don't know why yopu would want to use a 1/4" bit for a 3/4" wide mortise. You will be better off with a 1/2" - more sturdy.

[JayStPeter]

I recently built some benches. I used a 3/4" bit to make my mortises, but my methods for making tennons make square tennons. So, I knock the corners off with a chisel. That works fine for thinner stuff, but with 3/4" it was a lot of wood to take off. In the end, I had difficulty with uneven removal of material causing a slight shift in the piece. It would be nice to just remove a little from each corner as opposed to trying to make the end round and mistakenly changing the height of the tennon in the process.
If I go with a template guide based system, I'll be able to mix and match bits and guides and can try different combinations. Trying to hit the largest bit that will be acceptable is a good idea. I was stuck trying to remove the least wood from my tennons. Thanks for the virtual slap in the back of the head :D .

Jay