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View Karda's profile

Circle Jig help

by Karda
posted 05-06-2018 08:02 PM


33 replies so far

View Rayne's profile

Rayne

1025 posts in 1656 days


#1 posted 05-06-2018 08:27 PM

Need pictures of your jig to see where the issue might be.

View MrUnix's profile

MrUnix

6887 posts in 2316 days


#2 posted 05-06-2018 08:36 PM

What did I do wrong in making the jig.

Obviously didn’t measure right :)

Pictures would help. Circle jig for what? Router? Band Saw? Jig saw? Did you take into account the diameter of the pivot pin being used?

Quick fix would be to just make another pivot hole… or multiple pivot holes to get you different diameters.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View Karda's profile

Karda

1222 posts in 671 days


#3 posted 05-06-2018 11:37 PM

sorry the jig is for my band saw, the peg is centered at 5” heres a pic its on black might be hard to see.

View BFamous's profile

BFamous

156 posts in 238 days


#4 posted 05-07-2018 12:46 AM

I’ll believe tour peg is 5” on center to the blade, but it looks like there is about a 1×8” gap to the outside of the blade allowing for deflection as you turn your piece. Your blade is going to want to go straight, so I’ll push outwards as you spin.

Just my guess.

Though the “easiest” way to correct it, outside of making a new job, is go to a larger peg, bringing the center into 4 7/8”

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

View msinc's profile

msinc

497 posts in 620 days


#5 posted 05-07-2018 12:49 AM

The best way to have a circle jig for your bandsaw is to have the centering pin {for lack of a better term} on a slide. If you google bandsaw circle cutting jig there are several good youtube videos on the design. Having the pin on a slide is ideal because you can now set it for any size circle you want and you can double check that it is right with scrap and make any adjustments needed BEFORE you cut the piece you intend to use.

View GR8HUNTER's profile (online now)

GR8HUNTER

4552 posts in 829 days


#6 posted 05-07-2018 12:58 AM

simply make a jig for your belt/ disc sander then you will get perfect 10 inch circles or 9and15/16 :<))

-- Tony---- Reinholds,Pa.------ REMEMBER TO ALWAYS HAVE FUN

View Karda's profile

Karda

1222 posts in 671 days


#7 posted 05-07-2018 01:32 AM

I have thought of a moving pin but can’t find the track nor do i have the tools to make one. How is a larger peg going to work if the center is the same. I was going to plug hole but how do i measure so i don’t do it wrong again. Can’t do sander because this jig is for cutting bowl blanks

View Loren's profile

Loren

10477 posts in 3765 days


#8 posted 05-07-2018 01:59 AM

For a quick fix double-stick tape on the
back of a 10” square piece of ply would
do the trick. Put the pin in and test it.
Peel it off and re-tape until it’s where you
want and then screw or nail it if needed.

View Rayne's profile

Rayne

1025 posts in 1656 days


#9 posted 05-07-2018 02:24 AM

For a permanent fix, glue the pin or dowel in the hole, cut/sand flush, redrill with a brad point for a new pin. Just make sure to measure from the center of the Pin itself to the blade. If you’re using a tape measure to measure this, make sure to either account for the movable end-hook or start measure from 1. That end-hook moves 1/8”.

View woodbutcherbynight's profile

woodbutcherbynight

5545 posts in 2526 days


#10 posted 05-07-2018 03:07 AM



I have thought of a moving pin but can t find the track nor do i have the tools to make one. How is a larger peg going to work if the center is the same. I was going to plug hole but how do i measure so i don t do it wrong again. Can t do sander because this jig is for cutting bowl blanks

- Karda

Use a french cleat slide something like this.

attach a recessed ruler and you are in business. Even if it is off you can adjust after a test cut.

I built this from nothing but scrap I had on hand. Used a 1/4 drill bit end for my center dowel.

-- Live to tell the stories, they sound better that way.

View JBrow's profile

JBrow

1366 posts in 1037 days


#11 posted 05-07-2018 03:48 AM

Karda,

It is difficult to say what went wrong. Several factors occur to me that could affect accuracy, aside from an inaccurate measurement. The first two deal with geometry and the remaining with setup and technique.

The first could be from taking the radius measurement after the pin was installed and thus taken from the outside wall of the pivot pin. The radius measurement should be from the center of the pivot pin. If this is the problem then the radius of the disk would be larger by the radius of the pivot pin.

Second is that the point at which the blade begins cutting does not form a line that is perpendicular to the blade and intersecting the point at the center of the pivot pin. This could result in a radius longer than expected.

Third potential cause could be related to the blade. A ¾” wide blade cannot cut a 5” radius. Assuming a 5/8” or narrower blade, the blade could be flexing due to a dull blade, excessive feed rate, inadequate blade tension, and/or roller guides set too high above the workpiece.

Lastly, if the jig moved slightly during the cut, the radius could be off a little, but then the resulting disk would not be perfect round and would have been noticed.

One idea for correcting the jig without extensive reworking of the jig is to recut the kerf so that the pivot pin is 1/16” closer to the blade. This should result in the 10” diameter you are after. Moving the pivot pin closer to the blade by 1/16” would begin with clamping the jig to the band saw table in the position that resulted in a disk that was 10-1/8” diameter. If the jig has been repositioned since last used, the jig could be re-installed and a test cut made in some scrap and the resulting radius measured. In this case the thickness of the shim (below) would have to be adjusted to match the error.

Next a shim such as a long piece of scrap cut to a thickness of 1/16” can be held against the edge (opposite from the band saw column) of the band saw table while a fence (a straight piece of wood) is clamped to the underside of the jig so that the fence is snug against the shim and the shim is sandwiched tight between the edge of the table and the fence. With the fence clamped in place, it can be screwed to the jig. Once screwed in place the fence will be the thickness-of-the-shim away from the edge of the band saw table.

The jig can be un-clamped and removed from the band saw, and the shim set aside. The kerf in the jig can be re-cut by keeping the fence screwed to the underside of the jig firmly against the edge of the band saw table until the cutting edge of blade reaches the line from the center of the pivot pin. The fence can then be used to clamp the jig to the band saw table.

If the fence extends a few inches beyond the edge of the jig, engaging the fence and keeping it firmly against the edge of the band saw table may cutting the new kerf little easier.

View Karda's profile

Karda

1222 posts in 671 days


#12 posted 05-07-2018 05:33 AM

thanks everybody for you information, I plugged the hole and I’ll try again, maybe get it right this time. The thing that is so irritating is that I have made jig and got perfect circles. but now can’t

View msinc's profile

msinc

497 posts in 620 days


#13 posted 05-07-2018 05:49 AM


I have thought of a moving pin but can t find the track nor do i have the tools to make one. How is a larger peg going to work if the center is the same. I was going to plug hole but how do i measure so i don t do it wrong again. Can t do sander because this jig is for cutting bowl blanks

- Karda

Use a french cleat slide something like this.

attach a recessed ruler and you are in business. Even if it is off you can adjust after a test cut.

I built this from nothing but scrap I had on hand. Used a 1/4 drill bit end for my center dowel.

- woodbutcherbynight

That’s it!!!!! Not the only way to fly…...but definitely a way to fly!!!!! You might think you only have to cut one size circle and you can get it right the way you are doing it, but you will have to cut other sizes eventually. Might as well get it set up so you can perfectly adjust to whatever size you need when you need to do so.

View Woodknack's profile

Woodknack

12331 posts in 2497 days


#14 posted 05-07-2018 07:35 AM

For a 10” diameter circle, your radius must be 5”. It’s an unfair law of nature, like evolution and thermodynamics.

-- Rick M, http://thewoodknack.blogspot.com/

View Karda's profile

Karda

1222 posts in 671 days


#15 posted 05-07-2018 03:27 PM

I agree that is what I have 5” to the center of the hole yet it cuts over.

View gwilki's profile

gwilki

216 posts in 1591 days


#16 posted 05-07-2018 03:57 PM

Not to take this too far off solution, but why do you need to rough cut a bowl blank to “exactly 10”? Does your lathe have maximum 10” swing? In which case, the diameter could be any amount under, yes??

I have a jig with the pin moving in a T-track, so I can get the most out of a blank. However, since the final bowl is going to be smaller by some unknown amount than the rough blank, I don’t bother to measure the distance from the pin to the blade at all. That’s why I’m curious about your problem.

-- Grant Wilkinson, Ottawa ON

View Karda's profile

Karda

1222 posts in 671 days


#17 posted 05-07-2018 04:10 PM

yes my lathe swing is 10” I can use a little under for the 10”. But if I do it I want to do it right. I am thinking of other purposes where I want an exact measurement. Also for bowl blanks the smaller sizes can be over

View gwilki's profile

gwilki

216 posts in 1591 days


#18 posted 05-08-2018 12:07 PM

I think you will solve your problem following the advice you’ve received already.

Be sure that your distance is from the exact center of the locating pin to the inside of the blade. You are only out an 1/8”, so if you are out 1/16” measuring from the center of the pin to the inside edge of a tooth on the blade (not the flat side of the blade), your circle will be off by 1/8”. Depending on the set of your blade, if you measure to the flat of the blade instead of to a tooth, you could be off that much.

Also, made sure that the middle of your pin is in line with the back of the gullet on your blade. That measurement, too, will affect how accurate your circles are.

-- Grant Wilkinson, Ottawa ON

View Karda's profile

Karda

1222 posts in 671 days


#19 posted 05-08-2018 07:06 PM

thanks for the information about measurements, one thing I didn’t think of is the bloc ks I cut are often uneven chainsaw cut. the block may be quite al one side the the other

View Woodknack's profile

Woodknack

12331 posts in 2497 days


#20 posted 05-09-2018 03:35 AM

The blank moving up and down will change the cut radius.

-- Rick M, http://thewoodknack.blogspot.com/

View Karda's profile

Karda

1222 posts in 671 days


#21 posted 05-09-2018 03:44 AM

any suggestions thanks

View gwilki's profile

gwilki

216 posts in 1591 days


#22 posted 05-09-2018 01:15 PM

If your blanks rock, as Rick said, the radius will change somewhat. You can hot melt glue wedges to the blank to even if up, but with respect, I would say “don’t bother”. These are rough turning blanks you are playing with. As long as your lathe can swing them you are going to be turning them perfectly round = smaller anyway. You do need to deal with too big, but a bit smaller than your lathe’s swing should not be a concern. You will never get a 10” bowl from a 10” blank, no matter how good a turner you are.

WRT other pieces that you want to cut round and be reasonably accurate, I’m guessing that they likely start as squarish boards. With them, you don’t have the wobbly blank problem that you have with logs, so the other advice you have read here about getting your jig accurate should address your concerns.

-- Grant Wilkinson, Ottawa ON

View Kelly's profile

Kelly

2073 posts in 3061 days


#23 posted 05-10-2018 06:36 AM

Keep in mind, if your starting point is other than straight across from the pivot pin, the blade will want to wander.

My jig allows me to mount a square pieces of wood on the pin and they can be larger than the end circle. I just feed the piece into the blade, following the miter slot, then, when the sled hits a stop, which positions the pin across from the front of the blade, I just start spinning and get quick, dead on circles.

View hairy's profile

hairy

2750 posts in 3649 days


#24 posted 05-10-2018 04:59 PM

Watch this video. It’s the best circle jig I’ve seen. I followed his plan and it works great.

https://www.youtube.com/watch?v=Uem-9Wz1Dt8&t=819s

-- My reality check bounced...

View Kelly's profile

Kelly

2073 posts in 3061 days


#25 posted 05-10-2018 05:41 PM

hairy, that is the exact same jig I posted above. Mine just cuts bigger circles, has the cut outs to reduce weight on the cantilevered side, and uses a T track, rather than the very clever shelf bracket.

Note that the left of mine and his extend to the upper bandsaw support. This both acts as a counter-balance and reduces the dust problem others have when their circle jigs stop at the blade.

Key to both is, as mentioned, the stop, which allows you to use any size wood, unlike the stationary jigs, which require a square the same dimension as the diameter of the circle.

View Loren's profile

Loren

10477 posts in 3765 days


#26 posted 05-10-2018 06:39 PM


Watch this video. It s the best circle jig I ve seen. I followed his plan and it works great.

https://www.youtube.com/watch?v=Uem-9Wz1Dt8&t=819s

- hairy

The guy in the video has the right idea. Good use
of salvage materials. Anytime I make a jig for the
first time I try to use whatever collected junk I
have on hand to try out the idea without spending
any money.

I suppose with the jig extending past the table you
could use something like a upside-down t-track and
put a clamping knob underneath.

View Andybb's profile

Andybb

1225 posts in 720 days


#27 posted 05-11-2018 12:11 AM

Don’t want ro read all of the responses but in case nobody has said it the pin needs to line up with the back of the bandsaw blade, not the teeth.

-- Andy - Seattle USA

View Karda's profile

Karda

1222 posts in 671 days


#28 posted 05-11-2018 05:00 AM

thanks for the video, that is the way I will go. Bur I will need to use .5 inch ply. any suggestions on a track for wood that thing. how do I cut the dados I don’t have a router why is lining the pin up with the back of the blade better than the back of the tooth thanks Mike

View MrUnix's profile

MrUnix

6887 posts in 2316 days


#29 posted 05-11-2018 06:38 AM

Don t want ro read all of the responses but in case nobody has said it the pin needs to line up with the back of the bandsaw blade, not the teeth.
- Andybb

Is that how your’s is? That is the opposite of just about every article I’ve seen on the subject, like this one at Popular Woodworking magazine.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View AlaskaGuy's profile

AlaskaGuy

4354 posts in 2426 days


#30 posted 05-11-2018 06:44 AM



Don t want ro read all of the responses but in case nobody has said it the pin needs to line up with the back of the bandsaw blade, not the teeth.
- Andybb

Is that how your s is? That is the opposite of just about every article I ve seen on the subject, like this one at Popular Woodworking magazine.

Cheers,
Brad

- MrUnix


Brad is correct.

-- Alaskan's for Global warming!

View Loren's profile

Loren

10477 posts in 3765 days


#31 posted 05-11-2018 07:04 AM

I thought it was the front of the teeth. At the very
least starting the cut with zero or near zero material
on one side of the blade and the bulk on the other
can cause blade deflection. I’ve never made this jig,
but my understanding was the best practice is to push
forward for a bit until the blade is fully supported
in the cut and then start turning.

View hairy's profile

hairy

2750 posts in 3649 days


#32 posted 05-11-2018 02:45 PM



Watch this video. It s the best circle jig I ve seen. I followed his plan and it works great.

https://www.youtube.com/watch?v=Uem-9Wz1Dt8&t=819s

- hairy

The best part of this jig is that you can adjust the jig after it’s installed. It will move the jig towards or away from the blade, a very desirable feature.

You can make it without cutting dadoes.

Use 1/2” ply as a base, glue 2 pieces of 1/2 ply on top of the base, with your guide bar between them. The bar might be slightly below the ply, but you could shim it if it’s a problem.

I used T track instead of shelf bracket. I put a 1/4” 20 nut in the track and use an allen screw to set the size.

-- My reality check bounced...

View Andybb's profile

Andybb

1225 posts in 720 days


#33 posted 05-12-2018 02:08 AM


Don t want ro read all of the responses but in case nobody has said it the pin needs to line up with the back of the bandsaw blade, not the teeth.
- Andybb

Is that how your s is? That is the opposite of just about every article I ve seen on the subject, like this one at Popular Woodworking magazine.

Cheers,
Brad

- MrUnix

Brad is correct.

- AlaskaGuy


Hmmm. Well in Brad we trust. I thought it was the rear but I built mine 4 years ago but haven’t used it since.

-- Andy - Seattle USA

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