bandsaw problems

[xbgthardtop]

Hi just brought a new bandsaw ,hare and forbes bp300
https://www.machineryhouse.com.au/Products?stockCode=W420
and set it up according to the manual(so i think). I am cutting pine blanks 150 mm high using circle jig and a new 4 tpi blade 1/2 inch wide. The problem is that the cut starts and has a nice verticle cut but midway through the cut it the cut curves and I get a keg shape rather then a cylinder. Any help would be greatly appreciated as im lost. :doh::?

[Skew ChiDAMN!!]

Without much thought I can think of two possible reasons:

1. Impatience. You start off nice and slow but, as the cut progresses, you start "hurrying" the wood through... (Been there, done that, will do it again. :-)

2. Possibly your blade is just a tad undertensioned, so as it heats up & expands during the cut it's losing tension & beginning to belly out. I'd try increasing the tension a turn or two and see if it still does the same thing on the next cut...

[xbgthardtop]

I was a little bit cautious on my first ones. But probably got a bit keen on the next. Patience is not one of my better points. How do you tell if your tension is correct ?
Would a thinner blade help. I thought the back of the blade might be binding on the wood. :?

[Tex B]

There are a number of ways to tell if your blade tension is correct, but one is to see if the cut is straight. If it's not (as you've described), increase the tension a couple of turns and see if that works.

Some people pluck it and listen (but I have no ear for pitch so doesn't help much). Other people push to one side with consistent pressure and test the deflection (this will also depend on the amount of unsupported blade, how much pressure, etc).

For me, it was tighten/loosen/tighten until everything worked, then pluck, push, feel the tightness of the tightening screw (how hard to turn) and try and replicate that next time.

Does seem to be more of an art than a science.

Tex

[xbgthardtop]

Thanks for the help. Looks like I'm of to the shed to play tunes. Will keep you posted.:cool:

[Skew ChiDAMN!!]

Would a thinner blade help. I thought the back of the blade might be binding on the wood. :?

That's easy to test for... try cutting a straight line through the same wood. Along the grain. If it doesn't belly out, then obviously the curve has something to do with it and a thinner blade may help.

Another possibility, esp. if it's the blade that came with the BS (usually a "cheapie") is that the teeth aren't set correctly; have more set on one side or are blunter on one side than t'other. This'll also cause it to tend to belly out and will also cause the blade to constantly want to wander off the cutting line in the same direction, even when ripping along the grain.

The obvious test for this is to buy a new blade or two, same spec's, from a supplier with a good rep and do another cut. If that fixes it, send the old blade off for a sharpen/reset. (You can never have enough spare blades... so when one gets blunt you can simply swap it out and keep going while the blunt one is sent off for sharpening. :wink:)

If it doesn't, you're back to looking at the tension...

[DJ’s Timber]

Your tpi could also be too much for 150mm thickness. You'd need to be going pretty slow to allow the gullets to clear.

I'd be using a blade with less tpi for that depth particularly if you're going to be doing a fair bit of cutting at the thickness.

[weisyboy]

if its the blade that came with teh saw throw it out and get a better one.

the blades supplied witht eh hafco saws are useless.:2tsup:

[xbgthardtop]

All thanks for the help once again. The blade I have on at the moment is a new starret 3 tpi. Sounds like the tension is wrong . The gullets look clear. I was a bit cautious with the tension on the blade when I put the new blade on as there was no details on it in the manual. Still might buy a 6mm blade to get easier turns. And some new bearings for the pulleys as they are shot after only a couple of hours use.

[weisyboy]

All thanks for the help once again. The blade I have on at the moment is a new starret 3 tpi. Sounds like the tension is wrong . The gullets look clear. I was a bit cautious with the tension on the blade when I put the new blade on as there was no details on it in the manual. Still might buy a 6mm blade to get easier turns. And some new bearings for the pulleys as they are shot after only a couple of hours use.

id be ringing h&f and complaining about teh bearings in teh pulleys.:2tsup:

[joe greiner]

For turning blanks, you don't really need to cut circular. Eight or sixteen tangents is sufficient. A truly circular blank won't be perfectly mounted anyway, and when starting the turning cuts, you'll get one thump per revolution. Eight or sixteen thumps is a little smoother.

Whether cutting circular or tangents, the blade set will last longer if you alternate the direction of rotation of the blank, so that the set is degraded more or less equally on each side of the blade.

The barrel shape cut is produced by too much side load on the blade. And/or insufficient tension.

Joe

[weisyboy]

didya get it fixed?

[Robomanic]

...
The barrel shape cut is produced by too much side load on the blade. And/or insufficient tension.
...

My thoughts too :roll:

Have you tried adjusting the position of circle jig pin? You may want to move it forward or back a little (parallel to the blade) to get the cut to meet at the right point, tangent to your circle. The tighter the curve and wider the blade the more sensitive it will be to this position.

Maybe by now your all sorted anyway :2tsup:

[xbgthardtop]

Hi again havent had a chance to get back in the shed yet. Work keeps getting in the way. Will probably get a chance on the weekend.

Robomatic: I have the pin center directly in line with the top of the teeth.
Is this the norm ?

[Sculptured Box]

Here is a site that has a wealth of information and advice for things to do with bs's
Bandsaws and Blades information sites (http://www.tonyward.org/index.php?option=com_content&task=category&sectionid=3&id=38&Itemid=90%22%3E)

[Robomanic]

Hi again havent had a chance to get back in the shed yet. Work keeps getting in the way. Will probably get a chance on the weekend.

Robomatic: I have the pin center directly in line with the top of the teeth.
Is this the norm ?

That is where I would start. Depending on the hardness of the wood, radius and blade width I would be prepared to place the pin level with the teeth, or try further back up to half blade depth.

In the past when roughing turning blanks from half round logs I found that on the same saw in the same session, when I started using the circle jig I got more belly out in the cut, but cutting freehand my sides where straight. I ended up leaving the jig and making a number of cuts as mentioned earlier to approximate a circle. That was because i was more interested in the turning than tuning the saw at the time though.

Good luck :2tsup:.