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Segment jig issues

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ScaredyCat

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I'm have some trouble with my segment jig that I made today and, I think, I've boiled my brain trying to bug fix it.

I was actually getting better results when I just screwed a bit of wood at 15 degrees to my cross cut sled :/



Same sled everyone knows about.



Results I'm getting





Checking both fences are 15 degrees.

So what now? I can't think of what I've done wrong so I can't think of the fix. Can anyone shed any light on this?





.
 

CHJ

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A couple of observations and questions:-

Your Jig, personally I would like to see the leading edge of the angled support fence right up against the blade kerf line to provide maximum support and resistance to the work 'swinging' in the direction of the cut from the pressure of the blade.

I don't see the need for two angled fences, surely just flipping the stock 180 gives you both angles.

What exactly is your problem, the 12 pieces not summing up to 360 degree, or the cut faces not being at 90 to the stock face.

I don't find eyeballing the protractor accurate enough without 'tweaking'

I either use a digital angle block to check the segment included angle, and nudge the angle to suit or a bit more trial and error nudge without the digital block help until closed 360 deg. is achieved.
 

Distinterior

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Here is my segment jig I made 2 weeks ago from scrap bits and pieces I had kicking around...

15906902650016919958596047638125.jpg


Get yourself one of these cheapish plastic Set Squares. All the 12 segment rings I've made so far have been bang on....
The advantage of using the Set Square is,....even if both fences are not at the identical angle to each other in relation to the saw blade, the overall angle of 30 degrees is correct so you will always get a full 360 degrees when all 12 segments are fitted together. :D
 

Attachments

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You need a much bigger protractor! The longer the arm, the more accurate the micro adjustment. I have seen a YouTube video of someone using laser pointer and the wall of the workshop to give them a silly amount of accuracy: https://m.youtube.com/watch?v=GOCwlHx7BBI

Perhaps less over the top would be printing a large protractor on an A4 sheet: this one seems scalable, but there are lots out there - http://www.ossmann.com/protractor/

Print it on paper, or acetate to be see-through, laminate it to be more durable, and attach to your jig.

(Edited repeatedly because of auto spelling assistance)
 

peter-harrison

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One cheat which I use sometimes for large circular mirror frames made from segments, is to get them as good as I can without boiling my brain, then gluing up 2 180 deg sections, then all I have to do is get the 4 unglued ends in 2 straight lines.
 

ScaredyCat

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CHJ":22qfdosq said:
I don't see the need for two angled fences, surely just flipping the stock 180 gives you both angles.
Using the two means you reference the piece you are cutting on the same face for both angles of the cut. It's meant to be super accurate.

CHJ":22qfdosq said:
What exactly is your problem, the 12 pieces not summing up to 360 degree, or the cut faces not being at 90 to the stock face.
The 2nd picture down, those 6 pieces should be forming an 180 degree semi-circle, one edge is flush with the MDF base, the other is not.

CHJ":22qfdosq said:
I don't find eyeballing the protractor accurate enough without 'tweaking'

I either use a digital angle block to check the segment included angle, and nudge the angle to suit or a bit more trial and error nudge without the digital block help until closed 360 deg. is achieved.
It's a shame because I got this protractor specifically for this task. Do you have a recommendation?

.
 

ScaredyCat

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peter-harrison":198rxbzm said:
One cheat which I use sometimes for large circular mirror frames made from segments, is to get them as good as I can without boiling my brain, then gluing up 2 180 deg sections, then all I have to do is get the 4 unglued ends in 2 straight lines.
Yes, I was sanding the edges flat prior to making this but I wanted to try and cut that part out and get the accurate cuts straight off.

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Yojevol

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Looking closely at your protractor setting, it's about a quarter of a degree off.
 

CHJ

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Your eyeballed protractor angle is not accurate enough for this project.
By using it to set two opposing fences you are compounding any error, If you only ever want to set to 15 deg. for twelve segments then a drafting protractor as already mentioned stands more chance of giving you a more accurate included angle.


I don't use a table saw, a chop saw suits my simple segment requirements, but I check my blade to fence angles by checking tests pieces with a digital angle gauge and try to keep cuts within a couple of tenths of a deg.
 

Distinterior

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ScaredyCat":ys7r6bvd said:
CHJ":ys7r6bvd said:
I don't see the need for two angled fences, surely just flipping the stock 180 gives you both angles.
Using the two means you reference the piece you are cutting on the same face for both angles of the cut. It's meant to be super accurate.

CHJ":ys7r6bvd said:
What exactly is your problem, the 12 pieces not summing up to 360 degree, or the cut faces not being at 90 to the stock face.
The 2nd picture down, those 6 pieces should be forming an 180 degree semi-circle, one edge is flush with the MDF base, the other is not.

CHJ":ys7r6bvd said:
I don't find eyeballing the protractor accurate enough without 'tweaking'

I either use a digital angle block to check the segment included angle, and nudge the angle to suit or a bit more trial and error nudge without the digital block help until closed 360 deg. is achieved.
It's a shame because I got this protractor specifically for this task. Do you have a recommendation?

.
It is super accurate SC.....But only if you set your fence angles correctly!

Seriously, get yourself one of those plastic Set Squares , you won't be dissapointed.
I made 6 rings with 12 segments and 3 rings with 6 segments by using that plastic square and all of them were spot on.
 

ScaredyCat

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Ok, I've picked up one of those plastic triangles from amazon and it works perfectly. Cuts parts now fit beautifully together.


Thanks everyone.. Jig is a big hit with me, I just feel so guilty about essentially wasting a load of wood to hollow out a bowl from a complete piece of wood. Now I can just spend a little more time and eliminate that waste.

Also, wood seems to be getting more expensive.

.
 
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