Having issues with my Jet Bench Mortiser

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Forum topic by HornedWoodwork posted 02-03-2015 09:46 PM 1139 views 0 times favorited 7 replies Add to Favorites Watch
View HornedWoodwork's profile


222 posts in 1719 days

02-03-2015 09:46 PM

Topic tags/keywords: mortiser jet jbm 5

Hi guys! I’m new to the forum, hope you can help me out a little

I just got a JBM 5 and I’m having issues with the bit getting very hot and blackening the tip. I’m also getting a lot of noise when the bit is raised, but not on contact with the wood. Also the bit walks out of square after a little while. Any tips on running this Mortiser would be great as I have a 6 panel project on the bench and I’m looking at 24 mortises.

If it helps I’m making 3/8 mortises 1 inch deep in maple.

-- Talent, brilliance, and humility are my virtues.

7 replies so far

View Hammerthumb's profile


2956 posts in 2480 days

#1 posted 02-03-2015 10:12 PM

I set the chisel tip in using a nickel spacer so the chisel does not bottom into the mortiser head. Then push the bit up until it contacts the chisel. Tighten the bit, and then loosen the chisel and push it all the way into the head and tighten.

The idea is to have the bit slightly lower than chisel, so the bit and chisel do not make contact. If not adjusted properly, the bit can overheat quickly. This can also lead to the chisel twisting slightly during use.

-- Paul, Duvall, WA

View HornedWoodwork's profile


222 posts in 1719 days

#2 posted 02-03-2015 10:41 PM

That’s a good trick, I was probably setting up with the bit loo low and then too high. Need to find that sweet spot.

-- Talent, brilliance, and humility are my virtues.

View CypressAndPine's profile


62 posts in 2312 days

#3 posted 02-04-2015 02:10 AM

You might already have it solved, but I’ll make a recommendation. Are you using the economy bits (the $10-15 ones)? If so, then that is likely your problem. I would recommend you purchase some expensive top quality ones (especially for maple). It will make all the difference in the world. You will also need the sharpening cones because the maple will dull them pretty fast.

Good Luck,

-- Cypress Jake, New Orleans

View TheFridge's profile


10859 posts in 1991 days

#4 posted 02-04-2015 03:22 AM

And if your bit and chisel are turning colors, they are getting way too hot. That’ll kill the temper and soften the metal.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View pauljuilleret's profile


107 posts in 2157 days

#5 posted 02-04-2015 11:55 AM

I have the Delta mortiser and I use a dime instead of the nickle works good for me learned this the hard way after burning the end off the first 1/4 drill bit was lucky I didn’t scrap the chisel just had to clean it up a bit was lucky found a place you can just purchase the bits only (woodworkers supply)

View HornedWoodwork's profile


222 posts in 1719 days

#6 posted 02-04-2015 12:22 PM

I am using the bits that came with the machine, so yeah they are el cheapos I’m sure. I’ll swap them out for some better bits. One more question, any benefit to lubricating the bit? Seems like any lubricant would likely transfer into the mortise and might compromise the joint strength by messing with the glue bond.

-- Talent, brilliance, and humility are my virtues.

View runswithscissors's profile


3071 posts in 2530 days

#7 posted 02-04-2015 08:28 PM

I’ve used Dri Lube on the bits. Doesn’t seem to create a gluing problem. The other guys got it right—your bit should not be contacting the chisel. Give it 1/16” of clearance. I learned this the first time I tried a DP accessory mortise setup, and burned the 1/4” chisel. My hardware store has little molded sanding cones that fit on rubber cones with 1/4” shanks. They work well for sharpening the chisels, and are much cheaper than the diamond variety.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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