On fitting new tyres to the bandsaw wheels.
Not mine, well I knew that mine needed some work when I bought it a few months ago, mainly new tyres and the guides refacing but its not really a problem. Just another job to be done.
Just a word on when you need new tyres, they’ll do a lot of miles but after a few decades on a machine that’s doing a lot of work some tyres wear or compress in the middle where the blade runs. The result being that the machine starts to spit the blade off forwards, or the blade wont stay in the guides, it will tend to move forward or heaven forbid, if you make a blind cut and try to pull the work back toward yourself the machine will spit the blade off forwards at you.
Whats doing this, is that bandsaws, with very few exceptions have crowned wheels. The middle of the tyre being “higher” is further around than the edges, the blade runs “up” to the highest point and will stay there as the wheel rotates, and when the tyre is worn to the point where it is hollow in the middle of course it runs up and out to the edges and off making a mess of the blade and your work.
Time to fit new tyres.
As part of my part time dayjob though right now I have a big old 1930s vintage bandsaw to get working properly. The machine is an English Wadkin 36in joinery shop bandsaw, 5 hp, 12in depth of cut, 36inch wheels and weighs in at around a ton and three quarters. Beautiful machine, stable, powerful and very well engineered.
After all these years though there is some wear and tear, and it shed a tyre the other day, plus its guides are not the originals and not doing well. They’ve been replaced with blocks of UHMW plastic ( Ultra high molecular weight ) which tends to heat up and wear very rapidly. Not good.
I’ll talk about these in another post.
This machine is in the workshop of King Tuhetia’s master carver. Its a magical place where wonderful traditional Maori carvings are being chiselled out of huge logs and slabs of wood. I’ll see if I can get some pics, but in the meantime I am part way through replacing the tyres on the big machine, and did my own little 1950s vintage 12in Walker Turner as a practice run while I had the primers and adhesives on hand.
The big 36in Wadkin at the Master carvers workshop, this will take blades from 1/4in wide to 2in wide, cut up to 12in deep, and with the right blade will go through 4in wood at walking pace.
Scroll work to mini sawmill, its a wonderful machine.
Some advice on getting tyres for your bandsaw. Trying to obtain genuine spares for a 1950s machine where the manufacturer is no longer in business, let alone a 1930s built machine is never going to work, so for these I went to a company who supply conveyor belting, and have all the materials and technology to make rubber and polyurethane belting to width and length from blank stock.
Here are the guys I use. http://www.hcdflowtech.co.nz/
There will be someone doing similar work in any area that has a reasonable sized manufacturing base, let your fingers do the walking through the Yellow Pages and you’ll find them.
Kerrin at HCD made up my new tyres for both machines, they’re not cheap, but then the machine wont run without them.
From their range of product I chose a 60 shore (a measure of compressibility of rubber or similar) polyurethane, and specified the thickness of the tyre from their range of sheet material. I chose material in both cases that was just a fraction thicker than the original as they did not have an exact match. Be aware that you need to be as close as you can to the original but not under, too thick and you’ll have problems plus your blades could then be too short.
I had very carefully measured the wheels by wrapping a low stretch string around the wheel, securing one end with masking tape then running the line around the wheel and marking it where the two ends crossed, taking it off and measuring it. Checking by measuring the diameter and multiplying by Pi. Circumference = Pi x D
You need to be very accurate with this.
You need your tyre to be slightly shorter than the circumference of the wheel, if not under tension it can bulge up and cause a bump bump as the wheel rotates the bulge past the blade.
If I’m using rubber, for a tyre that’s say 3mm thick I’ll use a figure for its length of circumference minus 6% but for thicker materials I’ll go to 4%. I use 3% in all cases for polyurethane.
If your machine has a shouldered wheel, that is a lip on each edge, more common on metal cutting machines than woodworking but it is known, the tyre needs to be maybe half a mm narrower than the distance between the inner edges of the lips, if its too wide, even the slightest amount, the tyre may bulge up at the edge which ruins the tracking.
HCD also supplied me with the specialist adhesive and primer for the job, you don’t need a lot of it and its not cheap. But again, if you have a machine that wont work otherwise, you don’t really have a choice. Buying it in a small quantity from HCD meant that I did not have to spring for a full 500ml can of each so that helped the cost a lot.
Having got this far, you’ll be sitting looking at the machine with its guards and doors open, wondering where to go next.
First, you don’t need to take the wheels off, but it pays to take the table and the guides off for access.
Find a way of stopping the wheels from rotating, a stick through the spokes might do it, or a helper holding them, there wont be much stress on the wheel it just needs to be held still while you work on it.
Strip the old tyre, a very sharp chisel will do this ( mind your helpers hands) , cut across the tyre, use the chisel to peel up the end enough to get a grip and pull letting the wheel rotate toward you as you pull. It will probably come off in chunks leaving bits on the wheel perimeter, no big deal, persevere until you have the bulk of it off.
Stripping the old tyre from the bottom wheel of my 12in Walker Turner machine, you cant see it from this angle but I've clamped a piece of wood to the back side of the wheel to keep it from rotating while I work on it.
Next, all traces of the old tyre and the adhesive must come off. I use a little 100mm angle grinder with a Norton flat abrasive flap disk on it.
I use a type 27 conical one which seems to give better access as its used at an angle rather than flat. http://www.nortonindustrial.com/uploadedFiles/SGindnortonabrasives/Documents/Catalog_PDFs/NortonCatalog-FlapDiscs-optimized.pdf
Wear safety glasses, these things are designed to shed little particles of abrasive as they wear and that stuff is very serious if you get it in your eyes.
This disc will clean off any chunks of the old tyre as well as the old adhesive, it leaves a polished surface but try not to remove any significant amount of metal. Especially important on aluminium wheels as these discs can remove metal quite quickly.
Cleaning off the rim with an angle grinder fitted with a Norton abrasive flap disc. All traces of old rubber tyre and the original adhesives have to be cleaned off as with any trace of oil or such.
When perfectly clean, wipe with a solvent that leaves no residue, I use MEKP but Acetone or even methylated spirits ( alcohol ) will do.
No trace of oil or any such to remain.
Try your tyre by dry fitting, remember the allowance for stretch. It should be like putting a big rubber band around a parcel in that you have to stretch it on.
Remove and ---
Paint a very thin film of the adhesive primer onto the rim of the wheel. Make sure that the film is very even, brush across then along. You don’t have much open time on this stuff so work quickly. LEAVE NO LUMPS.
Same will apply when putting the adhesive on. I use chip brushes by the way, throw them away afterwards.
Leave to cure for 2 hours minimum on a warm day, overnight if cool. Apply a second coat.
Note, where you have “joined” as you work around will leave a small area where the film is doubled up, make sure that you don’t “join” in the same place with the second coat.
Same waiting/curing time.
Now comes the tricky part.
Coat the rim with the adhesive, this is a very powerful contact adhesive and you only get one chance so read carefully here.
Applying the primer for the two stage adhesive system.
Have the tyre inside out, and coat with the adhesive. Hang up on a nail or such and leave to dry for the time that the manufacturers ( I use a Bostick system) specify.
Note, if you put the coated tyre down on its edge on a wooden bench, you may have a real problem when you come back and find that its stuck to the bench!
( No I haven’t but I’ve seen it done)
If you’ve not done this before, a helper will be very helpful. So to speak.
Wash your hands very thoroughly to remove your natural oils, and no do NOT use rubber or fabric gloves for this job, they’ll become a permanent part of the tyre.
You can touch this adhesive and not get stuck, it should be tack free (not sticky to the touch) at this stage, but will seriously stick to the primed and precoated wheel.
Flip the tyre back the right way with the glue inside. Place the tyre on the far side of the wheel rim for about 20% of the circumference.
It pays to work over the top of the wheel and toward you.
Making sure that the part of the tyre in contact with the wheel is properly lined up relative to the wheel edge, rub it firmly to apply pressure to the adhesive in that area.
Get your helper to hold the wheel while you take the tyre and stretch it by pulling it toward you, I do this in about 5 or 6 stages, pull, line up, put on with the pull still on, and rub to pressure the adhesive. The idea here is to spread the “stretch” that I mentioned earlier fairly evenly around the perimeter of the wheel.
If you don’t, you will have to put all of the “stretch” into the last little bit as you apply it and that’s not easy, plus the tyre will be unevenly tensioned and that may cause problems.
New tyres on, tracking the blade back and forth with light pressure on to "settle" the new tyres onto the adhesive.
Work around the wheel until the last bit, I find that last bit is easiest by twisting it so the near edge is in contact with the near edge of the rim, and rolling it on. Note that this adhesive does not really grab hard until it has pressure on it so you do have a little ability to shuffle it. Not much though, don’t count on it, try and get it right first time.
It may pay to practice the process “dry” a couple of times.
Leave it for a day, then put a blade on with low tension, run the machine using the machines tracking adjustment to move the blade back and forth on the wheels to apply even pressure over the whole tyre. Do this for maybe 10 mins or so.
Ready for another 50 years.
Leave for a day, and you’re rolling.