Feed rate control help

[Bruno of NH]

Is there anyway to bypass this so I can run the mill until the new switch comes in ?
The feed speed knob switch 

[newoodguy78]

Would a  variable speed switch get you going. I picked up one up from Napa this summer and wired it into a fertilizer meter that was run by a 12v motor,it worked well. Dealer wanted like 400 bucks for the control box. Ended up getting creative for about 10 bucks and some wire I already had. The one I used was for listed as used for a blower motor in a vehicle.

[newoodguy78]

I should add was able to make the motor work by eliminating the dial but it was all or nothing and ran too fast for what I needed. Good luck getting going. 

[barbender]

Bruno, is it just the dial (potentiometer)? If you just bypass it I think it will run full speed, just like your reverse. But you may be able to find a potentiometer locally.

[moosehunter]

I always keep an extra in my tool box. I can usually get through a sawing session by putting pressure in different directions on the knob. Then I can change it during a break.
mh

[Magicman]

Yes it is possible but my answer to your question is no.  Possible and practical are kin but they ain't brothers.

 I am seeing ~750 Ohms and the potentiometer appears to be linear.  It does not provide a varying voltage to the motor but rather controls the H bridge which supplies varying pulses of 12 volts to the motor.  Faster pulses = faster speed.  I simply do not see a practical way to control the power feed motor's speed.

Yup moosehunter, my spare is shown above.  ;D

[Bruno of NH]

I just ordered a couple 

[GAB]

Bruno:
When mine failed I removed it and using the markings on it ordered two on line.
Is there an electrical parts store locally that might be able to help you?
I suggest that you take a picture of it prior to removing so you know what wire goes where.
GAB

[Sod saw]

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The photo of MagicMan potentiometer (pot) show three lead wires connecting it to the rest of the circuit.

The 750 ohms that his meter shows is (I assume) with the knob turned fully clockwise.  It may be possible to substitute a fixed resistor (which has only two leads) in place of the pot, how will you determine what resistance value and where do you insert that fixed resistor in the circuit where a three lead pot was designed to go.

From practical point, you will probably not want to take a chance and damage the rest of the speed control circuits by inserting another device in the wrong place.

Cleaning the pot might be helpful. Sometimes they are just dirty.  A can of clean compressed air (electronic clean) might blow out dust.  Other times a can of tuner cleaner or contact cleaner can clean up the moving parts within the pot if squirted into the hole near the wires.  Most often, though, the thing is just plain worn out from use.

If it were me, I would be patient and repair the mill properly.  I always have other things that have been put off that I can mess around with while waiting for repair parts to arrive.

GAB was lucky to have found one that functions by looking at the marking on the back.  It normally does not work with all pot manufactures.   With the loss of local Radio Shack stores, most  places do not have access to these kinds of electronic parts any more.

What do other saw owners think?   Should we all keep a spare pot on hand in the event that this repair is required again?


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[Jim_Rogers]

What do other saw owners think?   Should we all keep a spare pot on hand in the event that this repair is required again?

When I order any replacement parts, if I can afford it, I order two, one to put in and one to put on the shelf for next time. Then when I use the one on the shelf, I order another one. This keeps me going and replaces the stock items on hand. I did with my spare pot, when mine broke down.
Jim Rogers

[Magicman]

The wires are color coded, red, purple, & brown so no way to not connect the replacement correctly.  The red is the center wiper and I was measuring from the outside to the outside.  I did measured from the wiper to each outside leg to determine that the potentiometer appeared linear.

My recommendation is still to sit back and wait for a replacement.

Jim, I am curious about your failure.  Mine have always become erratic with the forward movement.  I have never seen a complete failure.  Of course the reverse is direct and potentiometer is completely out of the circuit with reverse.  I am assuming that your reverse is ok?

[Bruno of NH]

Mr Lynn
My reverse works fine
I noticed this morning I had to turn it further to get the head to move.
I cut one log after lunch and no forward movement at all.
Checked the drum switch and it all tested out.
That's why I thought it was this problem. 

[Magicman]

Hopefully it is the potentiometer and not the H bridge. 

It wouldn't hurt to get Wood-Mizer tech support involved.  :P

[barbender]

Bruno, I'd check it over really well for a mechanical drag or binding. Whenever I've had to turn the pot up extra, I had something dragging. A frozen cam follower bearing is a common one. And the bind can overload the electronics and fey your H bridge. Learned that one the hard way😁

[Buck69]

Bruno, it sounds to me like a dirty pot. Its working but somewhat intermittent?
If the pot is not a sealed pot it can be cleaned with a product called Deoxit( comes in a small aerosol can)If it is sealed you can sometimes  squirt it around where the shaft comes out, or any seams to get the deoxit in the pot then turn the knob from off to wide open a bunch of times may have to squirt it a couple times.
The deoxit cleans oxidation from the wiper in the pot.
Its pretty good stuff.
I used it to clean the pots on audio equipment and tube amp pots from the 60's

[Crossroads]

Mr Lynn
My reverse works fine
I noticed this morning I had to turn it further to get the head to move.
I cut one log after lunch and no forward movement at all.
Checked the drum switch and it all tested out.
That's why I thought it was this problem.

Did you happen to try putting some of the dielectric grease on the drum switch contacts? Last time mine was acting similar to what you described, I ordered a new one, but then gave the contacts a fresh dose of grease and it has worked fine since.

[SawyerTed]

Don't overlook the possibility it is brushes in the feed motor.  

My LT35 acted up and all indications were the speed control.  Turned out to be brushes.  

It was intermittent in the forward direction and consistent in reverse.  Under load in forward (cutting) it would run, stop, go and jerk along until it didn't.  But in reverse it would run fine. 

The potentiometer is an easy replacement, brushes not so much. 

[customsawyer]

Another problem I have seen is where the wire goes into the brushes working loose. It will give you the intermittent operation.  With this weather I'm leaning towards a bearing.

[Magicman]

Which is why I leaned toward Wood-Mizer tech support.  There are many possibilities and those guys have seen it all and know where to test and what to eliminate.

A splinter wedged underneath a cam follower can do strange things, but I am assuming that the carriage is free because I got the indication that Jim finished sawing something after he had no forward power feed.  ??

Removing the power feed belt and eliminate several components.

[Bruno of NH]

All the cam follower bearings check out all move freely and none flat spotted.
Checked for obstructions again none found.
Move like normal in reverse
Waiting on speed switch 

[Peter Drouin]

Buy 4

[Magicman]

I only keep one because they are kinda pricey plus you get an indication with irregular feed when they are about to croak. 

[caveman]

MM, I appreciate you describing how they fail.  This may be on the list of parts we might be replacing soon, based on your description.  I'll have to check our spare parts to see if we have one on hand.  If not, we should probably order one.  They are $63.72 today.

[bigblockyeti]

That's a bunch of $$$$$$$$$$ for a $5 potentiometer!

[Peter Drouin]

I have a bunch of parts on hand, I lot of $$$ tied up, but, when you can't cut, That's more $$$$$$$$$$$$$$$$$$$$$$$
Out of your pocket.