Intermittent Feed Problem on LT35

SawyerTed · October 17, 2020, 06:46:47 PM

Tuesday I was sawing for a customer and started having intermittent feed problems. All the characteristics of a cam follower going bad. After two and a half years of heavy sawing I thought it time to replace the cam followers. So I did the top and bottom ones on Friday. And just to be sure replaced the feed speed potentiometer. Did not solve the problem. I now have spare parts.

It would saw s few passes just fine then start the start-stop-jerking. So I checked the feed motor brushes. Three were fine. One had a broken spring and was bound up. I am surprised that the brushes are failing at this point between 400 and 500 hours.

WDH · October 17, 2020, 07:46:47 PM

When it happened to me this summer, it was the Drum switch contacts. You will see the drum switch if you take the control box cover off and move the forward/reverse lever. You will see the contacts. They were not making good contact in reverse and needed a little adjustment plus some of that dielectric grease that is in the control panel box. You should see the grease if you take the cover off the control box. Woodmizer told me to be very careful, but to very gently bend the little metal arms with the contacts so that they make better contact and to apply a bit of the grease to the contacts. Solved my problem. I thought it was bad cam follower bearings, too, but that was not the case.

WV Sawmiller · October 17, 2020, 07:55:39 PM

I still have nightmares/flashback when someone mentions replacing cam follower bearings on an LT35 and keep seeing my mill head on the ground because I had mine elevated, off-center and not secured when I replaced mine. The first thing I suspect is the feed belt. I did have a drive motor replaced under warranty but don't know what the cause was with the motor itself.

I'll remind everyone again - be very careful as that bearing is all that is holding the mill head attached to the bottom rail so if you are working on it do not elevate it any higher than necessary and secure it with a chain or such before starting on it.

Southside · October 17, 2020, 08:21:40 PM

My first set of brushes didn't quite make 1000 hours. They were worn out at that point.

SawyerTed · October 18, 2020, 12:43:09 PM

WV Sawmiller I remember that horror story and it was on my mind when I did this. I put mine down on the travel pin and it didn't move. I did have to give a touch of up and down to realign the bolts to reinstall the bearing weldment that holds the bottom cam follower. As extra insurance I looped two straps around the head and held up by the loader forks with minimal pressure on the straps. Just enough to catch it if something went wrong.

It has been a process of elimination with the simplest items addressed first. The feed belt was my first thought too. Adjusted it and checked it twice, no change. Then the drum switch was the next item and I cleaned, greased and adjusted the contacts. No change there. That's when I checked the potentiometer and it did show a spot with an erratic resistance measurement around 10 to 11 o'clock. The feed would smooth out at 1 or 2 o'clock but that would be too fast to saw most of what I do. The bottom cam follower, once removed, was a little gritty feeling. That's why I went the direction I did.

I feel sure this brush is the culprit. The others look fair. The other issue is this brush and another were bound up and not moving in the slot under the spring pressure. You can see the spring on this one is broken. The actual amount of brush isn't worn away excessively.

YellowHammer · October 18, 2020, 03:19:42 PM

Yes, I think you have nailed it. Good job.

Durf700 · October 19, 2020, 06:32:37 PM

where is this part located on the mill? can you put up a few pics for some of us? what does it do?

SawyerTed · October 19, 2020, 08:04:06 PM

This part is one of four brushes that are in the power feed motor. This motor is the one that pulls head along for sawing via the long chain beside the main rail.

Here is a brief and conceptual description of what the brushes do. A DC motor requires brushes to conduct electricity from the stator (the windings in the stationary part of the motor) to the armature (the rotating part of the motor). The resulting opposing magnetic fields cause the armature (shaft of the motor) to start moving. The brushes conduct the electricity to different windings by way of a commutator (a segmented ring) on the armature as the rotation occurs, thereby making the motor continue to rotate as the opposing magnetic fields move from winding to winding. You did ask what the brushes do.

In the LT 35 Parts Manual look at the exploded diagram for the Power Feed Assembly - Part Ref # 20 is the motor. The brush kit is Part # 061794. The brushes are a replaceable item in the motor. When looking at the motor there are four large caps with a screwdriver slot. The brushes are under these caps. The brushes are "wear parts" made of some type of relatively soft self lubricating conductive material. I haven't worked heavily with electric motors in more than 30 years so my recollections may need correcting by others.

Durf700 · October 20, 2020, 12:39:58 PM

thanks. so its inside the drive motor. I was wondering where those came from. I had some inconsistent feeding but I replaced my feed belt and it cleared it up on mine. good to know about that though.

thanks!

WV Sawmiller · October 21, 2020, 10:01:44 PM

Mine would slip some and I'd have to give it a nudge to get it to "grab" and start moving. I checked and tightened the power feed belt yesterday and no more issues today.

SawyerTed · October 23, 2020, 09:39:33 AM

New brushes arrived yesterday.

What a new brush looks like.

Will know in a couple of hours if this does the trick.

SawyerTed · October 23, 2020, 01:17:41 PM

Saws smooth as new! 8)

WV Sawmiller · October 23, 2020, 10:00:02 PM

How hard was it to install and what is the process?

SawyerTed · October 24, 2020, 06:27:03 AM

Removing the drive motor requires removal of 4 bolts that hold the bracket for the drive assembly. Two bolts are through the bottom of the mast, two bolts are on the opposite end. The drive assembly will swing down so I used blocks to hold it up. I left the drive sprocket connected to the chain. Once the drive assembly is disconnected from the mast/head I pushed the mast/head away from the drive.

The pulley and wires (mark the wires to reassemble because the motor will work backwards if the wires are reversed) need to be disconnected then the three small bolts that are used to adjust the belt tension are removed to free the motor. Four caps with screwdriver slots are removed from the motor to access the brushes. The brushes should just pull out.

Total time from opening the toolbox to closing the toolbox is about an hour. It is not hard to do.

WV Sawmiller · October 24, 2020, 08:34:14 AM

Once you remove the cap with the big screwdriver slot does the brush just pop up and you pull it out? When you put the new one back in does it have to slide in a particular way or into a slot or such to get it in the right position? Do you have to glue or fasten the brush in place or just push the cap back on? I see the spring so I assume it is under pressure? Thanks for your patience. Glad it fixed your problem.

SawyerTed · October 26, 2020, 06:23:03 AM

The brush rides in the slot under spring tension and the cap just holds it in place. The brushes should just slide out when the cap is removed. Two required a tug with some needle nose pliers. No adhesive. I did clean the slots with some electronics cleaner and a rag wrapped around a small stick of wood. You want the brushes to slide freely in the slot so the spring makes the brush contact the commutator. Removing and reinstalling the brushes is basically a parts swap.