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Mortise machine won't come up to speed

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Forum topic by tblrxdave posted 05-08-2011 05:20 PM 1168 views 0 times favorited 10 replies Add to Favorites Watch
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tblrxdave

44 posts in 2045 days


05-08-2011 05:20 PM

Iv’e got a eleven year old Grizzly mortise machine that won’t come up to 3400 rpm. It is an induction motor so the only other electrical parts are the ON/OFF switch and the starter capacitor. Anyone have an idea what is wrong?


10 replies so far

View Loren's profile

Loren

7826 posts in 2399 days


#1 posted 05-08-2011 07:55 PM

Sometimes if motors haven’t been run in a long time they have a hard
time. I usually just run them for awhile with no load and they eventually
loosen up. Chances are your mortiser has sealed bearings in the motor,
but if somebody has squirted WD40 in there, the grease in the bearings
could get dissolved causing them to run rough.

-- http://lawoodworking.com

View richgreer's profile

richgreer

4525 posts in 1826 days


#2 posted 05-09-2011 02:40 AM

Most of the newer mortising machines (at least the bench top machines) run at about 1700 rpm. In my opinion, that is better. If your machine is not coming up to the specified 3400, be happy.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View EEngineer's profile

EEngineer

906 posts in 2365 days


#3 posted 05-09-2011 04:11 AM

Rich – what the hell kinda answer is that? If it is designed to run at 3400 RPM, it ought to run at 3400. The fact that other machines are designed to run at 1700 has nothing to do with it.

Dave – need hard numbers. You say it is not coming up to 3400, what RPM is it achieving? How are you measuring it? In general, the ideal numbers are 1800 and 3600 RPM. Without boring you with a lot of motor design particulars, these numbers come from the number of “poles” designed into the motor windings. The difference between the ideal and the actual running speeds (usually 1800 → 1725 and 3600 → 3450) represent losses in the motors themselves. Note that these are all “no-load” speeds, i.e. motor running without anything on the shaft. Reference this
not entirely technically precise but close enough for jazz.

Other losses in the system also cause a slower RPM, also. For instance, are you running the motor on a lower capacity extension cord? Extra resistance (due to higher gauge wire) will cause it to run slower. If you are running the mortiser on an 18 gauge extension cord, try a 12 gauge heavy-duty extension cord. If your line voltage is a little low, it also may not come completely up to speed.

Now it gets a little murkier. Are you sure that the motor is only capacitor start? If it is capacitor start – capacitor run, then the capacitor that is still in series with the start winding while running may be bad. A bad run capacitor will also cause low “no-load” RPM. Reference this for theory

Good luck! Let us know how this all comes out.

-- "Find out what you cannot do and then go do it!"

View buffalosean's profile

buffalosean

174 posts in 2138 days


#4 posted 05-09-2011 04:23 AM

dave, I don’t know anything about motors. but i was wondering, will the motor issue aside, how do you like the grizzly mortising machine, i’ve been considering purchasing one. I’m curious how well the xyz table movement is and overall accuracy. thanks, Sean

-- There are many ways to skin a cat...... but, the butter knife is not recommended

View patron's profile (online now)

patron

13181 posts in 2092 days


#5 posted 05-09-2011 04:32 AM

i have a floor model ‘sunhill’
i have to spin the chuck
as i flip the switch
(and exactly together)
and leave it on
till i need to reset it

i like EEngineer’s capacitor ideas
will have to check for that
but i only use it about once a year
and only remember it
when i go to turn it on

good luck fixing it
keep us posted

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View EEngineer's profile

EEngineer

906 posts in 2365 days


#6 posted 05-09-2011 01:04 PM

Patron -

Your problem sounds like a classic bad starting capacitor. It may also be a bad centrifugal switch inside the motor but I would bet on the cap.

-- "Find out what you cannot do and then go do it!"

View tblrxdave's profile

tblrxdave

44 posts in 2045 days


#7 posted 05-09-2011 03:57 PM

I was in the middle of a cut when the motor stopped turning. Major difference in RPM under no load.

EEngineer, Wow, Thanks for the info. I’m gonna call Grizzly to see what they say. It can’t be that hard to replace a new capacitor.

Sean, Can’t say much about the new mortise machine. What I’ve seen in the advertisements are a few new refinements. It still takes a liittle time to set up to ensure accurate cuts. Overall the machine makes some very clean cuts as opposed to mallot and chisel.

View buffalosean's profile

buffalosean

174 posts in 2138 days


#8 posted 05-10-2011 12:53 AM

thanks for the info dave, goodluck with your motor problem

-- There are many ways to skin a cat...... but, the butter knife is not recommended

View poopiekat's profile

poopiekat

3735 posts in 2486 days


#9 posted 05-10-2011 01:39 AM

I’m with cr1 on this! We used to have cartridge fuses on a 220V panel saw that would sometimes let go for no reason, inside the dedicated electrical box for this machine. Losing one feed would make the motor just sort of run, but poorly.

-- Einstein: "The intuitive mind is a sacred gift, and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift." I'm Poopiekat!!

View tblrxdave's profile

tblrxdave

44 posts in 2045 days


#10 posted 05-10-2011 01:38 PM

Here are the specs. 1/2 HP, 120 Volt, 6 Amp, 1 Phase, Class E, 2 Pole, 3400 RPM

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