bandsaw project help....

[jeff_1064]

I have an old delta / rockwell 14" bandsaw (28-290). I am trying to cut a circle about 14" in DIA in oak that is about 4" thick (Base of a floor lamp). I have a new 1/2" blade on it and have it tensioned to about 3/8" defelection. I am using a circle cutting jig...my problem is the blade keeps bending or deflecting in the wood as I am rotating it causing the blade to leave the guide bearings and fall off the wheels. Is my tension spring bad / old? Any thoughts?

On a different note...my machines are all delta / rockwell and are older than me by about 10 to 15 years (I am 26 ). The joys of being a high school shop teacher...

[Popeye]

My first guess would be tension, second would be adjustment on the jig. I snapped a blade because the jig had slipped to the point that rather than the center point being aligned to the front edge of the blade it was actually past the teeth. Was one of those forehead slappers. Or.... could be both. I'm sure others with more experience than I will chime in. Pat

[Thom2]

My initial thoughts if I'm understanding everything correctly ....

If you're using a circle cutting jig, the centerline of your circle most likely lines up with the leading edge of your blade. This is fine with a narrower blade, but a 1/2" blade would bind in the kerf as you feed the stock. (The kerf actually curves and catches the back edge of the blade, twisting it out of the guides) My first choice would be to back off to a 1/4" blade, but I think (dangerous word there) you could also make do by shifting your pivot pin so the centerline of your stock is closer to the center of the blade.

HTH

[jeff_1064]

I forgot to mention the second try was a 1/4" blade...

I think it is a tension problem.

BTW a 1/2" blade can cut a 2 1/2" radius. At least thats what "The woodworkers wall chart"

Thanks for the info.....

[Thom2]

BTW a 1/2" blade can cut a 2 1/2" radius. At least thats what "The woodworkers wall chart"

I wouldn't put much money on that ..... I've had 3/8" blades that wouldn't cut a 14" Radius ..... very frustrating.

If you can make that same cut freehand without the jig, I'd have to say your tension is fine. I'm still pretty well sold on the idea that setup on the jig is out of whack.

[LCHIEN]

I may be dangerous, too,
but certainly 2.5" circle with a 1/2" blade would be tight.
I think a 1/4" blade would be where I start.
The leading edge of the blade must be at the radial line from the pivot, or, the blade will be headed out of town (sorry, Thom) and twist for sure.

[Thom2]

The leading edge of the blade must be at the radial line from the pivot, or, the blade will be headed out of town (sorry, Thom) and twist for sure.

No apology necessary, the more I thought about it, the more I realized it probably won't work.

[Russianwolf]

causing the blade to leave the guide bearings and fall off the wheels..

Which direction is it going to leave the guides?

The angle of the top wheel may not be set correctly to keep the blade tracking under this force, but I'm still trying to figure out which way the blade is going.

[jeff_1064]

update...

I made a new jig...using a 1/4" blade I still can not make the cut. The blade will move forward on the wheel (leaving the thrust bearing...moving toward the operator). While this is happening the blade slightly cups (think cupping of a board) and leaves the bearing guide and causes the blade to fall off the wheels.

I am sure it is tension issues. the bearings are set so there is about dollar bill thickness between the blade and each bearing both on the upper guide and lower guide. Also I am raising the guide to the max height in order to make the cuts.


jeff

[JR]

Also I am raising the guide to the max height in order to make the cuts.

Do you mean the upper blade guides are not positioned immediately above the workpiece? They are positioned at maximum height? If so, that would be a problem.

JR

[Tom Miller]

Have you checked the drift of your blade/setup? That is, as you're making a straight cut freehand (i.e. no rip fence), is the natural feed direction parallel to the bandsaw table's right edge?

The line between your circle-cutting jig's pivot pin, and the blade edge needs to be perpendicular to this feed direction line, not necessarily your bandsaw table edge.

Regards,
Tom

[LCHIEN]

...Also I am raising the guide to the max height in order to make the cuts.


jeff

I think that's serious problem. The upper guide should always be positioned right above the work. Like much less than 1/2 an inch.

[DJehlik]

Jeff,
Do you have a good sized lathe that would handle a chunk that size? I'd be tempted to rough it out on the BS with several tangential cuts, then turn it round on the lathe.

Your machines are old enough to have real iron in them.

Dave, former HS teacher

[cabinetman]

I would go along with the 1/4" blade, and get a coarse blade like 4tpi or 6tpi. Using a 4tpi will keep you from pushing the stock. It doesn take much stress to get out of whack.



"I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

[jeff_1064]

The guide has to be at max. height in order to make the cut. There is about 1/8" between the stock and the guide. I am going to replace the tension spring ($2.99 from delta + $7.00 SH ).

My machines ARE pure iron....

Jeff