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Circle cutting jig for bandsaw

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Forum topic by Davevand posted 02-05-2019 08:22 PM 692 views 0 times favorited 12 replies Add to Favorites Watch
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Davevand

128 posts in 1345 days


02-05-2019 08:22 PM

Hi
I have made a circle cutting jig for my older Grizzly (Delta clone) bandsaw and the thing will just not work. As i cut the circle the blade will drift toward the center, it will bind the blade and stall the saw if I force it to cut a full circle . I have tried 3 different blades (3/16-10, 3/16-14 and 1/4-6) and they all do the same. I have tried more tension, less tension, moving the blade position in the cut, I am at a loss as to why it is doing this.

Just an FYI, the same jig on my Laguna 14|12 works perfectly with a 1/4-6 blade, I cut 16 3-1/2 in wheels with no issues.
I just like to keep a wide blade on my Laguna and a narrow blade on the Griz so I was hoping to have the jig work on the Griz.

Any ideas on what I can try?


12 replies so far

View WhyMe's profile

WhyMe

1177 posts in 2070 days


#1 posted 02-06-2019 03:08 PM

Do you have the center pivot point of the circle in alinement with the tooth edge of the blade. If the cutting edge of the blade is too far in front of or behind the center of the pivot point will cause the blade to twist.

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gwilki

322 posts in 1983 days


#2 posted 02-06-2019 03:11 PM

I would look at where the centering pin lines up with the blade. If your jig has a stop that rides on the front of the table when you are cutting, it may well be that the distance from the front of the table to the blades on your saws is not the same. So, on the Laguna, the pin is positioned properly – at the front of the blade – but on the Grizzly, it is not.

If your jig does not use the front of the table as its stop, then I’m all wet. :-)

-- Grant Wilkinson, Ottawa ON

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gwilki

322 posts in 1983 days


#3 posted 02-06-2019 04:07 PM

It looks like why me and I were typing at the same time. Great minds think alike. :-)

-- Grant Wilkinson, Ottawa ON

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Davevand

128 posts in 1345 days


#4 posted 02-06-2019 05:32 PM

Yes, I have the center pin lined up with the front of the blade, even tried moving the blade a bit forward and back. Same issue.

thanks

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gwilki

322 posts in 1983 days


#5 posted 02-06-2019 06:03 PM

Can you post a pic of the jig? Without that, I’m out of ideas.

-- Grant Wilkinson, Ottawa ON

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BFamous

322 posts in 630 days


#6 posted 02-06-2019 06:10 PM

If my memory of geometry physics is still good, the fact your blade wants to go in towards the center would tell me your center pin is too far front. The fact you say you’ve tried to move the blade front/back baffles me, because if you move the center pin to the back of the blade it should actually force your blade to go out instead.

-- Brian Famous :: Charlotte, NC :: http://www.FamousArtisan.com

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WhyMe

1177 posts in 2070 days


#7 posted 02-06-2019 09:53 PM

Once I have my blade set/riding where it needs to be on the wheels, I adjust the circle jig to the blade position. I don’t think you should be adjusting the blade position to the circle jig.

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bondogaposis

5540 posts in 2860 days


#8 posted 02-06-2019 11:43 PM

What is the radius of the circle you are cutting?

-- Bondo Gaposis

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Davevand

128 posts in 1345 days


#9 posted 02-06-2019 11:50 PM

I am moving the jig relative to the blade, not actually moving the blade
Circle jig


Fairly simple jig, the center runs in a dovetail that I can lock at different radius
The pin is in a 1-inch dowel centered on the dovetail slide

This pic shows the difference in the wheels, they are about 2-7/8 inches in diameter, the left wheel cut on Laguna, right wheel on the Grizzly. The Laguna is almost perfect circle and square, the Grizzly is tapered almost a 1/4 inch top to bottom and the circle is out of round by over 1/4 inch. These were both cut out of 2×4 so they are 1-1/2 inches thick

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BFamous

322 posts in 630 days


#10 posted 02-07-2019 01:37 AM

There’s a top to bottom taper on the circle cut on the Grizzly? Check that your blade is square to the table.

Easy way: cut into a 2×4 scrap, then flip it over and see if the cut lines up with the blade. I’m guessing your table is off a degree or two.

-- Brian Famous :: Charlotte, NC :: http://www.FamousArtisan.com

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Davevand

128 posts in 1345 days


#11 posted 02-07-2019 04:01 AM

That taper is caused by the blade drifting in more at the top then the bottom, the blade starts out square to the table. That wheel is also out of round by over a 1/4 inch.

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gwilki

322 posts in 1983 days


#12 posted 02-07-2019 01:54 PM

@Davevant: I can’t tell in the pics, but how is the blade supported? That is, what type are guides are you using?

Clearly, some force or another is deflecting the blade, both horizontally so that the circle is not a circle at all and there is a taper top to bottom. You’ve said the blade is properly tensioned and presumably, you know the blade is sharp, too, since you’ve tried various blades.

The usual sources of blade deflection are blade tension, blade sharpness, speed of cutting and support for the blade. You seem to have addressed all these.

I hope someone here smarter than me can provide a solution, because I’m out of ideas. This is not rocket science, but it’s got me stumped. I will be interested to hear what your solution is when you solve it.

-- Grant Wilkinson, Ottawa ON

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