Hollow Chisel Mortiser


chefmagnus@grics.net

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I need to make many 1" mortises for the decking of my longboat mobile base. I only have hollow chisel mortisers that go up to 1/2". I was going to insert a 1/2" spacer make all of the first row of mortises alternating plunges to make a 1/2" mortise then remove the spacer and make the second row alternating plunges until all the mortises are 1"x5-1/2". Is this the correct way to make these mortise or should I use the edge guide and make the mortises with a 1/2" bit in two passes and square up the ends with HCM. Or should I make a template of the mortise that I can clamp to the rails and then square the ends up with HCM,

 

Or should I use the dado blade and remove 1/2" from the decking ends and put it into a 1/2" mortise. I really would like to have a 1" of wood supporting the monster band saw. 

 

I saw frank howarth big band saw. His is twice the size of mine and 5 x the weight. 

 

 

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use a router.  just make sure you take shallow passes and your bit is tight.  you don't want to hit your shop helpers, tcarswell and illini40, with a flying router bit.    it is hard to make clean mortises using multiple passes on an HCM.  If you do, I'd actually make two rows of 3/8" or 7/16" (whichever you have) leaving a small amount in the middle to chop by hand. 

 

^^ This is some great advice, right here. :D

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Please do. I just did some experimenting with different mortiseing techniques while building my door. Here is what I found.

Router only: creates ridiculously smooth walls and a guaranteed depth of cut but I could not seem to square the ends without digging in at an angle and ended up with perfect mortises for wedging which was not my intention.

hCM: awesome tool but mine doesn't have a fence so it was very difficult to keep the sides clean without getting little ridges

Mortiseing by hand: I suck.. Like seriously..

HCM+router: best combo for me. I started at the very ends with the hCM to get the ends square and 90* then stepped in and down slowly with an up spiral straight bit and produced wonderful results..

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I have tried many different ways since I had lots to make.

1 By hand with mallet and chisels. I gave up before I ruined the rail that I was working on.

2 HIM has quick setup and gets the job done. In the beginning I had the HIM setup were the bit was in side the chisel so it was not working. I reset it and went through a mortise in minutes and spent a hour chiseling to get a smooth walled mortise.

3 Router with a jig and 1/8" collar. Took me an hour to build a jig that had the right sized hole. Can make mortise with round corners that I can't seem to make square by hand.

4 router with a edge guide made quick work of the mortise but I over shot the mortise by a bit and had to use the mortises to get the ends square.

4 make a square mortise at the end the router out in between. This produced a nice looking mortise but took 6 passes to get to 1.5" depth. Very slow. Took over 20 minutes a mortise.

5. Make the mortise with the mortiser and use a separate router to clean up each of the walls. Using two routers to get smooth walls got me done in less than 5 minutes a mortises. Also I could use the micro adjustment to tweak the mortise for a perfect fit.

I know that most people done have two router setups but for the second set of mortises I used the final method of the mortiser and two routers with edge guides set for the left and right walls. I used the mortiser to make rough mortises and then cleaned them up.

I did find a 1" spiral bit but I did not feel comfort

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The tenon is left over pressure treated decking. I did make a jig out of 1/2" plywood. But found it almost impossible to clamp to the sides of the bandsaw longboat. It is a glue up of 4 pieces of baltic birch plywood to give me about 3" of thickness. I made 10 ~1-3/8"x ~6-1/8" mortises. This is what I am using as the tenons, Severe Weather Max 5/4 x 6 x 12 Standard Ecolife Treated Decking from Lowe's. It is not very close to the 1" or the 5-1/2". I don't know if it is the boards that I got or what. They are in my leftovers pile and thought this would be a good use for them. 

 

If you know of a quick and easy way to keep a jig square, I would go back to the jig for cleaning up the sides of the mortises. I have the first five done now have to clean up the second 5. 

 

I plan on gluing and screwing into the ends of the decking after I drill countersink holes and pilot holes. Would you use 3 or 4 screws per board. Also since the boards are thicker than I was lead to believe, can you point me to a video or website for making a 1-3/8" dado with a 7/8" stacked dado? I need to make a dado for the decking in front and back 2x4.

 

Thank you if you can help. 

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I left a flat edge from the table saw as the edge that I was using the guide and fence on. If I had to do over I would have glued up only the two inner pieces and then made my mortises through with a scrap piece under them to prevent chip out. The routers make much smoother sides that slip together easily. But the corners don't fit the decking. I tried to make the corners square with chisel and felt like I was going to blow out the bottom of the mortise or I over shot the length of the mortise. I have both a plate jointer and a Festool domique but was afraid that it could not carry the ~600 lbs. And was uncertain about putting a biscuit into end grain. 

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