Troubleshooting a Slipping Drive on a Bandmill
Motor's running but the blade's not moving — what's wrong with this picture? Take a tour through the drive train and find out ... April 20, 2011
Question
I build furniture and added a Timberking 1220 mill to my arsenal last year. I've cut seasoned white oak, sweet gum, pine, cedar, and some 40" DIB red oak since I've had it. It's been a good mill and cuts great. I've never had problems cutting any of the above (unless the blade got dull). It has smooth consistent cuts with plenty of power.
Now I'm cutting some fresh SYP - small diameter (6-12") and I’m having problems. I've had to slow my feed rate way down due to the blade stalling (not the engine), and can easily stop the blade if I don't just creep along. The blade stops while the drive belt keeps turning (no slippage from the drive belt). I've increased tension on the blade but it doesn't help.
My conclusion is that the tires (really belts) are worn out and allowing the band to slip. What do you think? I've never replaced them. They are not glazed over, and stick up around 3/64-1/16" above the wheels, but that's the only thing I can think of. I've also tried two new blades, and the back of the blade doesn't even hit the thrust bearing when it stalls, so I don't the blade is the issue. I feel pretty confident the tires are the issue, but wanted to get a second opinion before ordering replacements. How do you all determine when to replace them? I plan to try Urethane (from Suffolk). Any opinions on them?
Forum Responses
(Sawing and Drying Forum)
From contributor A:
I use belts on my WM and have to change them about every three months, but I cut a lot. Do you know the set of the blades you are using? SYP will grab the blade if the set is not wide enough. Also the sap in SYP will cause the blade to slip. Use water that has about two shot glasses of Pinesol per 5 gallons of water to cool and lube the blade. It just needs to drip on there.
If the belts are not glazed then they are not most likely the problem. It does not hurt to change them as new belts will grab better and are taller. How do you measure tension on the blade? It could be a bit low which will allow the band to slip on the belts.
From contributor R:
Well you didn’t say exactly what type of belt you have, so I assume it’s an automotive type V-belt, and also I assume it’s a loose and sloppy fitting belt. If so, they use those because they go on quickly with little effort, and if you have approximately 19" bandwheels/sheeves, and the belts are loose, most likely their outfitted with B-57 belts, and that is not a 57" belt, it's a 60" belt. My mill was fitted with belts like this, and I didn’t like the slop or slap, so I went down 1" to a B-56 NAPA belt which is 59" and had to be patient and consistent while getting them on, but it has been worth it. NAPA belts have a crown, they’re not flat top.
Also one other thing, I have never had this problem like your describing, but possibly your blade lube in conjunction with your belts could be causing this issue. I cut SYP all the time and my mill just cuts right through it. I have no opinion on the Urethane belts, I just know what works and is tuff.
From contributor W:
I tried the Suffolk belts a few years ago. A bear to install and they vibrated like mad and broke two bands. Suffolk couldn't solve this problem. I would suggest as the others have a B56 belt from NAPA.
From the original questioner:
Thanks for the help guys. I'll try to provide a little more detail. Contributor A - I'm using Timberwolf blades, .045" 7/8 pitch with .027" set per side if my memory is correct (Suffolk's recommendation for SYP). Judging from the cut quality and amount of sawdust left on the board I think the set is adequate.
I am using water/Pinesol for a coolant/lubricant as you recommend. I run a small stream onto the blade. One thing I noticed was that I have more sawdust sticking to the tires (under the blade) than I normally do. I'm not sure if this would allow slippage or not.
The mill uses a compressed coil spring for tension. There is a red line that the manufacturer recommends tensioning to. When I first tried TW blades I ran their recommended flutter test and the tension setting was just shy of the red line. I've been running at the red line normally. This morning I went past the line to see if it helped (it made no difference). The tension spring is in good shape and there is no binding in the mechanism.
Contributor R - you are correct about the tires being V-belts on 19" sheaves; however, they are very tight on the wheels. There is no slack or slop in them. Thanks for the info on the NAPA belts.
Contributor W - thanks for your honest feedback. I am surprised about the vibration problem but am now glad I asked before ordering.
After thinking about it I plan to mark the tires with white paint in a spot and run the mill, stalling the blade. As soon as it stops I'll peek in the guards and see if the tire is still moving; that should verify if the tires are the problem. Any more ideas/recommendations?
From contributor I:
Glad to hear things are going well with your 1220 mill. SYP can be a bear to cut. Another possibility would be that your blade is acting dull due to build-up of sawdust and pitch on the teeth. The blade's sharp under all that goo, but the goo acts like a layer of home-made MDF and prevents blade from it cutting at its best. So lube is a possible issue (as others have pointed out) as well as just changing blades more than normal would probably help.
From contributor A:
Yes the blades should be fine. That is a good blade for cutting SYP. The blade may not be slipping on the belt but the belt may be slipping on the wheel. If the belt is worn and hitting the bottom of the groove then it may be slipping. Just get a set of B57 belts and see how it goes.
From contributor M:
I am trying to pull the sheave angles from memory but I think industrial belts have a 32 deg. angle and automotive sheaves have a 40 deg angle. I would not go to any automotive parts store and buy belts for your mill or if you do make sure they have the proper sheave angle. You can find a lot of industrial suppliers in the yellow pages to purchase belts from. I have talked to several 1220 mill owners that purchased belts at an auto parts store to drive their hyd. and the belts failed due to wrong sheave angle. When buying B57 belts you will find some brands will be a little loose especially if they have a letter after the B57 which means they were manufactured for export.
From the original questioner:
I've been very happy thus far, and I know I'll get this problem figured out. I've tried two different new blades with the same results, and am using water/Pinesol as a lubricant. I did check the teeth/tips/gullets, and they appear very clean.
Contributor A, thanks again for the help. Since the belts are not glazed I'm thinking they may be slipping as you mention (that's why I plan to try marking the belts to see if they're spinning with the wheel or slipping). I didn't have a chance to check anything today, but hopefully will get back on the problem tomorrow.
From the original questioner:
I went out today (with a fresh mind), put a small piece of masking tape on the tire/wheel, and fired her up. I opened the blade guard (don't do this!) so I could see, engaged the blade, and used a normal feed rate to stall the blade. Upon looking in, I found the wheel was not turning, so obviously the drive belt was slipping.
I had assumed (I know, I know) that the drive belt was not slipping since there was no squeal in the belt, but I assumed wrong. Opening the guard (again, don't do this!) allowed me to see what was really going on in there. I tensioned the belt and everything is working great again.
From contributor M:
I also made a mistake about the hyd. belts failing and the 1220 does not have hydraulics. I should have posted the 1600 model. Also if you have any vibration you may want to check the drive belt for what is called flat spots. Sometimes the pulley on the motor can cause ware on the belt while the belt is setting in one spot slipping.
From contributor A:
That is a lesson that you will not forget any time soon. Glad you can make sawdust again. Just look at all the stuff you learned that is not wrong with your mill. It was a good day at the mill here today. We only ruined 3 blades trying to saw out 4 mbdft of walnut.
From the original questioner:
Contributor M - no big deal! I figured you were talking about a different model. No vibration problems, so I should be ok.
Contributor A, there's always a good side to everything! As you mentioned, I now know more than I did so it was a good day. When I stop learning I guess I'll quit! Three blades for 4k walnut isn't too bad. Most of them I've seen have a lot of metal in them (usually from a yard though).
From contributor B:
I use a nylon ratchet strap to tension the drive belt on my 1220, works real well.
From the original questioner:
That's a great idea on the strap. I made a tensioner using some scrap wood, a T-nut and a bolt; not quite as quick as a strap, but it does work well.
