Owners of Hollow chisel mortisers - speed question

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Forum topic by TheFridge posted 05-28-2017 01:34 AM 1974 views 0 times favorited 9 replies Add to Favorites Watch
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10859 posts in 2292 days

05-28-2017 01:34 AM

Topic tags/keywords: resource question hollow chisel mortiser mortiser

I just acquired a 1 hp hollow chisel mortiser to clean up, fix, and put to use on a temporary basis. I plan on getting my own floor model when this one goes back to its owner some time in the future.

All that being said. 3460 rpm for this and some others I looked at sounds way too fast for the bits. Especially since a lot of chips and very little clearance between bit and chisel is involved.

Do any owners find that a bit fast? Sounds like it should only be 1/3 as fast. I’d probably be happy with a 1730 if it came with it. But it didn’t

Any recommendations for a 1hp 14 FLA single phase 120v to single phase 120v vfd? If I were to get one I’d put it on my personal whenever it’s time to give the one I have now back.

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

9 replies so far

View MrUnix's profile


8160 posts in 3005 days

#1 posted 05-28-2017 02:19 AM

Doubt you can use a VFD on it. There are only a few special type single phase motors that would work (PSC, shade pole and synchro). A typical single phase induction motor found on 99% of all machinery won’t work. You could of course swap it out with a three phase motor though :)


-- Brad in FL - In Dog I trust... everything else is questionable

View TheFridge's profile


10859 posts in 2292 days

#2 posted 05-28-2017 02:30 AM

Well. there’s foor for thought. Never been in a situation where I really though I needed to slow a single phase motor down. Thanks.

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

View HerbC's profile


1805 posts in 3665 days

#3 posted 05-28-2017 04:08 AM

I have a ShopFox bench mortise. It has a 3/4 HP motor that runs at 3460 rpm. I have been quite satisfied with performance once I polished and sharpened the chisel bit set.


-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View pintodeluxe's profile


6176 posts in 3619 days

#4 posted 05-28-2017 04:19 AM

Both my Delta bench top and Jet floor mortisers are 1725 rpm. I use the Jet most often, and it purrs like a kitten. It’s basically the same as the Powermatic, and I’d recommend it if you can find one.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View TheFridge's profile


10859 posts in 2292 days

#5 posted 05-28-2017 04:34 AM

I sharpened the bits and gave it a whirl. It had a tendency to smoke if very light cuts weren’t taken while doing the mortise but by bit.

I might try looking for a slow speed motor. Only problem is that it’s flanged mounted but it is what it is. I think I’d be happy with a 1700ish rpm.

I appreciate the info guys.

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

View bonesbr549's profile


1588 posts in 3873 days

#6 posted 05-28-2017 01:13 PM

I have a floor model PM, and dependinig on the wood, I get a burn ocasionally and if chips are bindig and not ejecting it can be a problem. I have that problem sometimes on cherry.

However, I suspect a couple things.

1) You could have a slightly bent bit. Whats the brand?
2) Try this, when you fire it up keep a piece of beeswax or canning wax and just touch the bit and coat it a bit. That could help. I do this a general practice.
3) Inside your chisel, there could be a burr. Take a dowel and wrap in some sandpaper and work the inside a chisel to take care of it. (depends on brand)
4) Do you have a chisel cone. Make sure you work your chisels and hone the inside with the cone. I got a really good one (brand escapes me at the moment), and I use my stones to hone the outsides and get them mirror sharp. This helps by reducing the force you use and it aides in chip extraction as you are not forcing it into the material to cut.
5) I had a problem when I first got mine, that I was not being careful when I tightened my bits in the chuck, and was running a little out of true and that was causing a screaming issue. A good sign you will have the burn problem.

Those are just some ideas. Good luck.

-- Sooner or later Liberals run out of other people's money.

View TheFridge's profile


10859 posts in 2292 days

#7 posted 05-28-2017 01:46 PM

There is runout in the bit I have. Also have a couple different diamond cones coming from LV.

I’m gonna get some new bits but I don’t want to tear them up.

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

View JBrow's profile


1368 posts in 1726 days

#8 posted 05-28-2017 05:09 PM


I have the Powermatic 719T floor standing hollow chisel mortise. The motor plate states the motor spins at 1720 rpm.

Porter Cable found that traditionally hollow mortising machines used a 3450 rpm speed to drive the auger bit. These higher speed machines cut mortises faster but were prone to smoking and overheating and even bluing of the tooling. The slower machines were introduced to reduce overheating but resulted in slower cuts. So there appears to be a trade-off – fast and stress or slow and relaxed – but evidently both speeds work well when cutting mortises. Here is the article (“Tool Test: Benchtop Mortisers”). It provides some interesting additional information, some of which would apply to both benchtop and floor mounted hollow chisel machines.

I believe that it is important to reduce heat build-up in the tooling, whether running the auger bit at 3450 or 1720 rpm. One way to reduce friction and the resulting heat build up is to ensure the auger bit spins freely without rubbing against the chisel. One way this can be done is by 1) locking the chisel in place using a dime or quarter as a spacer that keeps the chisel from properly seating; 2) securing the auger bit in place snug against business end of the chisel; 3) then removing the coin and fulling seating the chisel. This provides that free space. This method results in very little squeaking when the machine it turned on and the tooling does not blue. While the auger bit cuts a little deeper hole than the chisel, I have not found this to be much of a problem.

I have also adopted the practice the lubricating the auger bit with a very light coat of machine oil after I have finished using the machine. Since a very light coat of machine oil is applied to the auger bit only, I have not noticed any problems with glue keeping the mortise and tenon joint together.

View TheFridge's profile


10859 posts in 2292 days

#9 posted 05-28-2017 11:34 PM

I’d rather not roast my bits personally but I will only shell out so much for a lower speed setup. There’s no point to me in buying premium bits if there is really good chance of overheating it with general use.

Suggestions about lubricatting are duly noted.

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

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