# Pivoting fence arc vs distance?



## Bogydave (Nov 14, 2008)

Question is a little long.
Since I have a stationary pivot on my fence, can I use it to calculate distance at the bit as I swing the loose end?
If I measure an equal distance (distance from center of the bit to pivot) in a straight line with the center of the pivot bolt through center of the bit, on the other end of the fence , then mark an arc, using the pivot. Each 1" of the arc should be 1/2" at the bit.
Now, knowing the front of the fence is forward (x distance) of the pivot center, equal on both ends of the fence, is there any offset involved.
If I carried the arc (at the loose end of the fence) forward 2", would the fence be flush with a 1" bit?
I'll experiment a little tomorrow, but if this is set up accurately (like a rip fence marker on a table saw) this could be used for many applications.
Common used stops could be drilled in the benchtop (drop in a pin) and make the next cut. (every 1/2" equals 1/4" at the bit)
Maybe this is already done (just not on my top & fence)
My next top may have a curved side the radius of the pivot fence.
Anyone ever experimented with this or a similar approach?


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## mcelduff (Dec 20, 2007)

I am using a 2000m long fence pivoted at 2000mm from the free end with the router bit at1600mm from the free end. So this gives me approximatly a 5 to 1 scale advantage i.e. 5mm rotation at the free end gives 1mm movement at the bit. I say "approximatly" because the mathematics is not as simple as it first may appear - this because the pivot point is a) offset from the face of the fence and b) the fence is normally offset from the bit. To determine accurately the amount of pivot movement at the free end to give the required movement at the bit involves some tricky maths of the trigonometrical variety

You can get over this by reference to a programme downlodable free from the internet for use with a pivot fence The programme produces a scaled A4 printout of the actual movement at the bit based on distance from bit to an arbitrary baseline and the distance from the pivot point to the same baseline at the end of the fence. You then tape the printout to the table and pivot the fence according to the scale. With the above fence layout and using this programme (which comes with full pdf instructions) I can achieve accuracy to 1/100” (0.20mm). You can find the programme called RouterScale at tunelabworld.com. 
I haven’t actually set this up yet but would like to hear the comments of the experts out there before I comit..


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## allthunbs (Jun 22, 2008)

Hi Hank and Dave:

Interesting diagnostic process except you forgot something. Although the distance from the bit to the fence appears to be a straight line, in actual fact it is an arc. You will have to divide that arc into accurate increments and then mark those increments accurately on the table surface.

One of you referred to the scale on a table saw as being accurate. Sorry, it isn't for a whole bunch of reasons. First of which is parallax. Second your reference point is suspect everytime you move your fence. The only way to be accurate is to use setup blocks. These are precision representations of distance. For example:

http://www.leevalley.com/wood/page.aspx?c=2&p=45089&cat=1,240,41064

is what I use for all critical setups, no matter what the tool. Router Workshop has something similar, but without the 1-2-3 block.

Neat idea but fraught with problems, configuration, setup and use.

It would be interesting to see your implementation should you decide to continue.

BTW, I'm no expert, just trained to look for the problems before they happen.

Allthunbs


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## mcelduff (Dec 20, 2007)

I am aware that the locus of the movement at the fence is an arc. I expect the RouterScale programmers recognised this fact and included it in the maths but I have no way of knowing this without access to the underlying code from the developers. 
The RouterScale programme takes care of the scale i.e. suppose you wanted a 10mm bit to be offset from the fence by 70mm (arc distance as you point out above) for a dado route then all you do is input this into the programme and press the print button. What you get as output is a scaled up printout which you attach to your table and move the fence the desired amount according to what the scaled printout tells you. Subsequent offsets can be read off directly without the need for any further reference to the programme. The print out even gives you a scale verification check for x and y coordinates so you know if there is any problem with the print. 
I recognise that accuracy of setup is one issue to be considered but as master craftsmen (which we all aspire to) this will be in our genes anyhow.

Hatchet Man


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## bobj3 (Jan 17, 2006)

Hi Dave

You may want to take a look at the drawing below,,, don't make it to hard ,this is a tried and tested way of making the pivot fence work for you .


Note*** the slot that's running parallel to the front side of the fence is in place so you can swing the fence back off the backside of the router table so you can remove/replace the insert in the fence easy with out removing any item that is in place on the front of the fence,feather boards,holds downs,bit guards,etc. 

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Bogydave said:


> Question is a little long.
> Since I have a stationary pivot on my fence, can I use it to calculate distance at the bit as I swing the loose end?
> If I measure an equal distance (distance from center of the bit to pivot) in a straight line with the center of the pivot bolt through center of the bit, on the other end of the fence , then mark an arc, using the pivot. Each 1" of the arc should be 1/2" at the bit.
> Now, knowing the front of the fence is forward (x distance) of the pivot center, equal on both ends of the fence, is there any offset involved.
> ...


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## allthunbs (Jun 22, 2008)

mcelduff said:


> I am aware that the locus of the movement at the fence is an arc. I expect the RouterScale programmers recognised this fact and included it in the maths but I have no way of knowing this without access to the underlying code from the developers.
> The RouterScale programme takes care of the scale i.e. suppose you wanted a 10mm bit to be offset from the fence by 70mm (arc distance as you point out above) for a dado route then all you do is input this into the programme and press the print button. What you get as output is a scaled up printout which you attach to your table and move the fence the desired amount according to what the scaled printout tells you. Subsequent offsets can be read off directly without the need for any further reference to the programme. The print out even gives you a scale verification check for x and y coordinates so you know if there is any problem with the print.
> I recognise that accuracy of setup is one issue to be considered but as master craftsmen (which we all aspire to) this will be in our genes anyhow.
> 
> Hatchet Man


Hi Hank and Dave: Now, the next step is that you're going to remove the fence to change bits. You might even change base plates. Now your baseplate has moved, your bit has moved which means you're going to have to recalibrate your fence. You would be further ahead with the setup blocks. Given how often I change bits, I would dare say you would be spending all your time calibrating your "instant" direct measuring fence.

My suggestion is that you watch Rick and Bob use a stick as a fence and in 1 easy move, get it exact with their "fine adjusting tool!" I have three reserved for the purpose, they're that good.

Now, I read the RouterScale manual and I find it interesting the job that they cite as raison-d'être for their project, box joints. While you're watching Rick and Rob, check out their box joint jig. No need to calibrate your fence for each cut. Rather than spend the time for a one-off fence calibration, make yourself a box joint jig. Route 1 rabbet, cut 1 sub fence, glue it together and drill 1 hole, clamp to the router table and make a box joint.

Allthunbs


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## bobj3 (Jan 17, 2006)

HI allthunbs

No need remove the fence to change bits or pop out the mounting plate ,just swing it out of the away..

No need to recalibrate the fence with the stop block on the back side of the fence,, once the fence is put back in place the stop will let it sit right back in the same spot..quick and easy...

That's the neat part about using the swing type fence.. 
You could call it the OP fence on steroids 

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allthunbs said:


> Hi Hank and Dave: Now, the next step is that you're going to remove the fence to change bits. You might even change base plates. Now your baseplate has moved, your bit has moved which means you're going to have to recalibrate your fence. You would be further ahead with the setup blocks. Given how often I change bits, I would dare say you would be spending all your time calibrating your "instant" direct measuring fence.
> 
> My suggestion is that you watch Rick and Bob use a stick as a fence and in 1 easy move, get it exact with their "fine adjusting tool!" I have three reserved for the purpose, they're that good.
> 
> Allthunbs


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## allthunbs (Jun 22, 2008)

bobj3 said:


> No need remove the fence to change bits or pop out the mounting plate ,just swing it out of the away..
> 
> No need to recalibrate the fence with the stop block on the back side of the fence,, once the fence is put back in place the stop will let it sit right back in the same spot..quick and easy...
> 
> ...


Hi bob: You mean that if I change from a 1/4" bit to an 8mm bit, the fence automatically recalibrates the distances from the bit? And if I change from a 1/4" spiral to a 1 1/2" round over, it will adjust accordingly? BTW, that last change requires that I change baseplates. That moves my collett about 1/32" because of the mounting differences on the two baseplates.

Allthunbs


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## bobj3 (Jan 17, 2006)

HI allthunbs

Most/Many router bits use the same size bearing ,if we are talking about apples to apples...
" 1/4" spiral to a 1 1/2" round over" no , then it will need to be readjusted .Let's say a R & P set, it automatically recalibrates the fence..

" change baseplates "  it sound like you have one of the lame OP base plates setups  that you need to fix, with just a bit of rework..
OR buy one more router for your OP system, then you don't need to change out the plates,, It took me a long time to get what Bob and Rck R. did on the show, they have many ,many routers ,you will never see them switch the plate just pickup a new router with the right base plate in place.. 


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allthunbs said:


> Hi bob: You mean that if I change from a 1/4" bit to an 8mm bit, the fence automatically recalibrates the distances from the bit? And if I change from a 1/4" spiral to a 1 1/2" round over, it will adjust accordingly? BTW, that last change requires that I change baseplates. That moves my collett about 1/32" because of the mounting differences on the two baseplates.
> 
> Allthunbs


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## allthunbs (Jun 22, 2008)

bobj3 said:


> Most/Many router bits use the same size bearing ,if we are talking about apples to apples...
> " 1/4" spiral to a 1 1/2" round over" no , then it will need to be readjusted .Let's say a R & P set, it automatically recalibrates the fence..
> 
> " change baseplates "  it sound like you have one of the lame OP base plates setups  that you need to fix, with just a bit of rework..
> OR buy one more router for your OP system, then you don't need to change out the plates,, It took me a long time to get what Bob and Rck R. did on the show, they have many ,many routers ,you will never see them switch the plate just pickup a new router with the right base plate in place..


Hi Bob:

What's an R&P set?

OK, how does one "fix" an OP base plate? I have four routers now and I'm forever swapping baseplates around. One router = one function? Even if I won the lottery, I'd never have enough cash to assemble such a collection and once I've got it where do I put it?

I have 7" and 11" baseplates and I'm about to start to manufacture my own special purpose ones.

Allthunbs


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## Bogydave (Nov 14, 2008)

I see it's not a simple as I thought or hoped.
BJ, I wondered what the bolts spider was, now it makes sense. I guess you could make a few spiders that has 4 step downs for various uses. A block of wood would do the same thing with faces different distances from the center hole.
I realize that once it is set up, if anything is changed the calibration is off.
Maybe I'll just use a tape measure, test cut, re-adjust, test cut etc before routing the piece(s) needed. But for the common cuts, I'll make some fence stops. It'll just take some time to get them calibrated for the fence & table I have using KISS principle.

Not as simple as I first thought when it was rattling around between the ears in the idea stage.


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## bobj3 (Jan 17, 2006)

HI Dave

Yep. The type below works just as well and it's a lot essayer to make 


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## dovetail_65 (Jan 22, 2008)

I am not quite sure what is not as simple as you thought.

Using a pivoting fence is extremely simple with bit changes if that is what you are partly referring too.

Just put in the bit, take a straight edge put it on the fence and pivot until the straight edge touches the bearing, lock down the fence and done. Takes maybe 30 seconds.

I just love the pivoting fences.

I was having a hard time following your initial post, but possibly this explanation helped even if I am off base..


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## Bogydave (Nov 14, 2008)

BJ that's KISS principle at it's best. 
Like the knot in the board, adds class. 

My thought was that you could put marks & make box joints, dovetail joints etc in a say 6" wide board & just move the fence in increments.
Pivot fence is great, was thinking of how to have it be even more so.

What bearing?


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## dovetail_65 (Jan 22, 2008)

If you are using bits with bearings thats all.


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## bobj3 (Jan 17, 2006)

Hi Dave

" knot in the board " I just hate to waste walnut 

You could stick on one of the rulers tapes,, The spider I have setup for 4 diff. bits sets,, the neat thing about it you can use it on bits without bearings it's always hard to set them up but once you have it's easy to pull the fence back to that point and your set to make the pass,,,many bits don't have bearings as I'm sure you know..  the CMT table comes with off set bars that made it easy to use the bits without bearing... 



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Bogydave said:


> BJ that's KISS principle at it's best.
> Like the knot in the board, adds class.
> 
> My thought was that you could put marks & make box joints, dovetail joints etc in a say 6" wide board & just move the fence in increments.
> ...


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## Bogydave (Nov 14, 2008)

BJ
I'll set something like that up for sure.
Yea, setting one up when using a bearing as the distance isn't an issue, it's the myriad of other bits & uses I'm looking to set accurate distances for. (& have repeatability)

I like knots, you know it's real wood. I used one for the handle on the router table door.


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