thumbsucker 11th May 2016, 10:45 PM I am needing advice I wish to use a router to cut some mortices using a jig and a guide bushing. Now I will be making through mortices.
Now as I understand it. While a down cut spiral will leave a cleaner crisper entry will it do the same on the exit of the mortice vs a upcut? Or is an upcut better for through mortices?
NCArcher 11th May 2016, 10:52 PM I would have thought you would be better off using an upcut to clear the chips as you cut. Depending on the thickness of the workpiece you are unlikely to be attempting to cut the full mortice in one go.
thumbsucker 11th May 2016, 11:10 PM Yes mortices would be progressively cut moving down ~ 3mm on every pass.
Yes an upcut would help clear chips better but my interest is in surface quality on both the entry and exit sides of the mortice.
pippin88 11th May 2016, 11:12 PM Can you swap bits half way through? (That's what I would do on the CNC Router for best results, start down cut, swap to up cut).
thumbsucker 11th May 2016, 11:21 PM Can you swap bits half way through? (That's what I would do on the CNC Router for best results, start down cut, swap to up cut).
I did think of that idea but it means I would have to buy to bits and I would have to swap bits out. Doubling my workload.
Think I found the answer
Both leave a clean cut, but where down-cutting bit (http://woodworking.about.com/od/bladesbits/qt/AlignForstners.htm)s tend to leave a very clean top edge but rough bottom, an up-cutting bit leaves a clean bottom but somewhat rougher top edge.
Using Spiral Router Bits and Straight Router Bits (http://woodworking.about.com/od/bladesbits/qt/SpiralStraight.htm)
Since I value appearance and a clean crisp mortice on both sides.
I think if I am doing a through mortice - I should glue some sacrificial MDF to the exit end of the mortice then use a down cut. This will give me a clean entry and the sacrificial MDF will give me a clean exit, once removed.
I will have to take it slow to allow the shop vac to extract chips, but its a small price for crisp mortices.
Thoughts?
Also if this photo is accurate then downcut is the way to go.
379160
Lappa 11th May 2016, 11:24 PM Yes mortices would be progressively cut moving down ~ 3mm on every pass.
Yes an upcut would help clear chips better but my interest is in surface quality on both the entry and exit sides of the mortice.
I clamped a piece of timber underneath when I did a through mortise. I used an upcut spiral bit. Bottom edge of mortise looked fine.
hmmm - writing as you posted :D
pippin88 11th May 2016, 11:25 PM Or perhaps the opposite - sacrificial piece on top and use an up cut bit.
However if you glue a sacrificial piece, you are going to have to remove some material due to this. How will you do that? Sand? Thicknesser? Could you just use this finishing process to remove the slightly poor edge on one side without bothering with the sacrificial bit / gluing?
Will one side be covered by a shoulder anyway? In which case does it matter if that side has a slightly poor edge?
thumbsucker 11th May 2016, 11:59 PM sacrificial piece can be chipped off with a chisel and a hand plane shaving does quick work removing any recent mdf.
I think a little experimentation maybe in order.
Kuffy 12th May 2016, 01:23 AM I would use an upcut bit. I have never noticed any excessively ragged edges which wont be removed with final smoothing. Furthermore, if the mortise is parallel to the grain, it wont leave a ragged edge at all.
thumbsucker 12th May 2016, 11:37 AM Thank you Kuffy.
elanjacobs 12th May 2016, 02:45 PM What Kuffy said. Also, down spirals aren't designed to plunge
thumbsucker 12th May 2016, 05:17 PM Now my search is on for an uncut spiral bit that is long enough but will either fit an 1/4" or 8mm collet. 8mm bits come in longer lengths but are harder to find.
elanjacobs 12th May 2016, 05:47 PM Carbitool make an 8mm bit with a 25mm cutting length. The total length is 63mm, so you could probably cut to 40mm deep if you have enough plunge travel.
Kuffy 12th May 2016, 06:05 PM I use a CMT 1/4" solid carbide upcut spiral bit. part number: 191.008.11 (1" cut length, 2 1/2" overall length).
I plunge through my mortising jig, which is 18mm thick, and then create a 25mm deep mortise (which is only just deep enough for a 1/4" mortise). 43-44mm deep is about as much as I can go without doing something silly like inserting the router bit into the collet by only 12mm, which will ruin the collet pretty quickly.
elanjacobs 12th May 2016, 06:47 PM without doing something silly like inserting the router bit into the collet by only 12mm, which will ruin the collet pretty quickly.
Not to mention the likelihood of the bit coming out and ruining your whole week...
Xanthorrhoeas 12th May 2016, 08:46 PM What about using a compression bit? I don't have one, and have never used one, but I have read that they give the cleanest surface top and bottom as they effectively combine an upcut at one end spiral with a downcut spiral at the other end.
Glenn.Visca 12th May 2016, 08:49 PM A mortise chisel ? Tee hee [emoji3]
elanjacobs 12th May 2016, 09:19 PM What about using a compression bit? I don't have one, and have never used one, but I have read that they give the cleanest surface top and bottom as they effectively combine an upcut at one end spiral with a downcut spiral at the other end.
When you're using the full cutting length at once (or at least enough to get past the 8-10mm upcut part) they're great, this is why they're used for cutting melamine and veneered board.
If you're only cutting in small steps to get to the required depth, you're really just using an up spiral but with a whole lot of down spiral on top of it to get in the way of chip ejection.
You can get compression bits for mortising with a shorter up section, but it's still about 6mm so unless you're going to at least 7-8mm on the first cut I don't think there's much to gain.
IMO, they're more suited to automatic machines like CNC routers and dedicated mortisers or something like the Multi Router ( JDS Multi-Router - Mortise And Tenon Machine - Woodworking Router (http://jdstools.com/product/multi-router/) ) where the router is fixed and you move the piece on a table.
Jeff Leslie 12th May 2016, 10:37 PM I might be wrong but the pics show the effect of both bits when cutting effectively a trench at 45 degrees across the wood. I do not see any plunge cuts. I used to use my Leigh FMT plunging full depth in steps with a final clearance route using up cut bits. Nice bit of kit and has been mentioned, any tear-out from the entry (which I doubt will occur anyway), will never been seen so why worry? Exit is the main concern,yes????? Note also that both Domino machines use up=cut bits and the entry cuts fine, straight off the tool. Can't recall ever having to clear the mortices.
lesmeyer 15th May 2016, 01:31 AM I have an 8mm solid carbide upcut spiral bit made by ONSRUD in the USA. It has a 31mm cutting length. Purchased from Lee Valley.
Les
aldav 15th May 2016, 10:42 AM 379160
The problem with this demonstration is that that's NOT a mortice it's a dado. Downcut bits are naturally better for dadoes, that's what they're designed for.
As indicated by other posters when using spiral upcut bits for mortising the correct method is to perform a series of overlapping plunge cuts to full depth and then clean out the remaining waste in two or three passes. You will get a very clean mortise with virtually no breakout at the top edge.
Unless I missed it you don't state how deep these mortises will be. Although you can get longer cutting lengths in 8mm and less diameters of upcut bits the longer the cutting length the more careful you need to be to not put excessive sideways pressure on the bit (that is, when performing the final clean out passes) or you may break the bit.
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