Yet Another Narrow Rip/Cross Cut Fixture

[enderw88]

[EDIT]  I have posted a far more detailed description of operation and construction below

I have seen a few ideas for repeatably cutting pieces narrower than the MFT Rail, but they all cut on the right side of the blade, which seem very anti-Festoolian to me, not to mention asking for kickaway (TS-X5 version of kickback).  Obviously the big problem with cutting strips narrower than the MFT rail on the left side of the blade is making sure the cut is parallel to the opposite edge.  Here is a fixture that handles that task:

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It consists of a base board with two t-tracks perpendicular to the working side.  In each track is fitted a narrow aluminum pointer that indicated the thickness of the cut.  Next to each track is a ruler held down by rare earth magnets (I stole that idea from somewhere here, I can't remember who now, but thank you!)  To set the fixture lower the MFT rail and move the fixture in until the working edge is flush against the working side of the guide rail.  Slide the pointers in until they contact the back side of the rail and tighten them.  Lift the guide rail and slide the rulers until they just kiss the pointers. This zeros the jig.  Now slide the pointers to the wide of cut that you want and slide the fixture beneath the guide rail, you can now position your workpiece and be certain the the cut will be parallel to the edge hidden beneath the rail.

The advantage this fixture has over the others I have seen is that the guide rail system is design to give the best cut on the left side, and this fixture control that side of the workpiece.

It can also handle repeat tapers.

 

[Ned]

Could we see a picture with the guide rail in working position?  I think I understand, but that pic would help a lot.

Ned

 

[Brice Burrell]

  Ned, I think the bits sticking up on the jig go behind the rail (left side) and act as a stop for setting the width of the rip. I have a very simple version of this type of jig made from scrap. 

 

[enderw88]

I'll try get a picture while it is in use, but my MFT is tarped over supporting a fiberglass layup right now, and I can't get to it.

Brice was correct.

 

[iggy07]

Craig  -

I vaguely understand what you are getting at, and the end result sounds great, including the ability to taper repeatedly.

I also see the jig, but I have some questions about how it was constructed.

Beyond that, I (unfortunately) have no clue what you are describing regarding the set-up and use of the jig . . . ?!

Further details would be greatly appreciated, including pics at each step along the line. I realize this will take some time, but I think this would of considerable interest to other members, and of course, that's the whole point of these forums.

It looks like an excellent procedure!

Thanks,

Ed

PS - I just read about your current project - take your time, and give us pics when you have an opportunity!

 

[enderw88]

The first task is to calibrate the fixture to the guide rail you are using.  This shouldn't change much if you always use the same one, but it is easy to check and shouldn't be skipped.

So, grab the fixture and slide it underneath the guide rail, like this (note that the pointers and ruler are in meaningless positions right now:

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Loosen the nuts on the pointers and slide them back, this will allow you to set the working edge of the fixture flush against the working edge of the guide rail, a suitable piece of wood can help in this, but using fingers is also very effective:

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Once the working edge is flush with the rail, slide the pointers in until they push against the back of the rail and tighten the nuts.  The pointers are now calibrated to give you a zero thickness cut (useless, but essential)

Continued...

 

[enderw88]

Now that the pointers are adjusted we adjust the rulers to the pointers. In the next picture we see that the ruler is slightly shy of the pointer. This could be because we are using a different guide rail from last time, or the rulers drifted on their magnets since the last time it was used 

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Slide the rulers until the ruler is exactly at the pointer, like this:

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Now that the fixture is calibrated to the rail, setting up to make a narrow cut of a specified width is simple.

Continued...

 

[enderw88]

In this picture we see one of the pointers set at "2" on the ruler, setting both pointers the same will give you a 2 inch wide cut across the rail

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After setting the pointers, put the fence beneath the guide rail and slide in your workpiece.  Ensure the pointers are firmly against the guide rail, and the workpiece is firmly against the fixture.  Standard practice with respect to supporting the guide rail across its width still applies.

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This shot shows a piece of wood with a pencil line where the cut would be (note that my rubber piece is shot so the line isn't particularly straight, but it is parallel to the back edge.

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[enderw88]

Construction details:

Base is 3/4" plywood from the scrap heap.

Route two parallel dadoes to hold the tracks.  It is critical that these dadoes are perpendicular to the working edge. The distance between them should be as great as possible, this reduces inaccuracies during setup.

Tracks are Rousseau T Tracks, anything similar would be acceptable, the only requirements are that they are straight, and can hold the pointers when the pointer nuts are tight.  The tracks are epoxied into the dadoes as there was only about 3/16" left in the thickness of the plywood.

The two pointers are from scrap 1/16" aluminum I had around from another project.  The only thing critical about the pointers is that the vertical edge be square to the base, you could get away with only using one hold down nut per pointer if you are pressed for resources.  Using sheet metal has the advantage of being close to a knife edge which reduces inaccuracies over using thick stock.

The rulers are held down to the base using 1/8" diameter rare earth magnets.  The rulers themselves are stainless steel (yes they are magnetic, it seems no one is able to make non-magnetic stainless steel any more) 12 inch ruler cut down to 7.25 inches.  THey have metric on the reverse sould you want go euro.

 

[Chris N]

Let me start out by saying that I am no expert when it comes to jig making.  My jigs are never this nicely made.  Nice work Craig and very nice summary.  Thanks for sharing it.

I really like this fixture and the concept.  The concept is very similar to what Jerry Work puts forth in his paper: Advanced Cutting and Routing Techniques using the MFS Multi Routing Template.

My only thought for an improvement is that if the jig had only two relatively small points of contact with the work piece (instead of the entire length of plywood shown), it would minimize the opportunity for "foreign material" on the working face of the jig (dust, chips, etc) to spoil the accuracy and repeatability of the cut.

 

[Corwin]

My only thought for an improvement is that if the jig had only two relatively small points of contact with the work piece (instead of the entire length of plywood shown), it would minimize the opportunity for "foreign material" on the working face of the jig (dust, chips, etc) to spoil the accuracy and repeatability of the cut.

It is possible to create your jigs with the two point contact as you prefer, but that will define the minimum length of piece that it will be usefull for unless you make the distance between these contacts adjustable.   Hmmm, that's doable.

While this jig looks to have its uses, it does not look capable of creating truly parallel cuts.  To obtain a parallel cut you I need more accuracy than one I can set by eye with a scale -- I've gotten lucky a time or two with an 8' setup within .005" of parallel -- wish I could do that all the time.  

For shorter parallel cuts on the MFT, simply use a square of MDF and place a low fence on the surface parallel to the cut line.    This serves as a sled that you can position left/right along your MFT's fence to locate the fence atop the jig the needed distance from the cut line.  If you have scales on your MFT's fence you can readily set your width of cut.  This type of jig can be used on either side of the blade if you like, and you can use it for various thicknesses of material -- place like thickness material on other side of jig's fence to provide proper support for guide rail.

At some point you need a different arrangement for longer cuts.  I am currently working a few things in this department, so I'll have to wait 'till later to comment...

What I am curious about is just how parallel are the cuts in the 4' and longer range.  And what tolerance is reasonable.  Maybe I am too picky but if cuts are not within .010" or so of being parallel I feel I need to do a little more homework...

Corwin

 

[enderw88]

My only thought for an improvement is that if the jig had only two relatively small points of contact with the work piece (instead of the entire length of plywood shown), it would minimize the opportunity for "foreign material" on the working face of the jig (dust, chips, etc) to spoil the accuracy and repeatability of the cut.

It is possible to create your jigs with the two point contact as you prefer, but that will define the minimum length of piece that it will be usefull for unless you make the distance between these contacts adjustable.  Hmmm, that's doable.

While this jig looks to have its uses, it does not look capable of creating truly parallel cuts.  To obtain a parallel cut you I need more accuracy than one I can set by eye with a scale -- I've gotten lucky a time or two with an 8' setup within .005" of parallel -- wish I could do that all the time. 

That is quite a feat!  You are correct that I probably cannot be better than 1/32 across the length of the fixture using the rulers. Although, what I will probably do is use my combination square as a story stick from the working edge to the fence pointers, that should get me well beneath a sixty fourth, assuming the guide rail doesn't doesn't drift due to vibration.

For shorter parallel cuts on the MFT, simply use a square of MDF and place a low fence on the surface parallel to the cut line.    This serves as a sled that you can position left/right along your MFT's fence to locate the fence atop the jig the needed distance from the cut line.  If you have scales on your MFT's fence you can readily set your width of cut.  This type of jig can be used on either side of the blade if you like, and you can use it for various thicknesses of material -- place like thickness material on other side of jig's fence to provide proper support for guide rail.

At some point you need a different arrangement for longer cuts.  I am currently working a few things in this department, so I'll have to wait 'till later to comment...

Yes.  I am planning on a four foot long version when the need arises. Although something like story sticks that mount onto the guide rail and come around the back may be a better solution.

What I am curious about is just how parallel are the cuts in the 4' and longer range.  And what tolerance is reasonable.  Maybe I am too picky but if cuts are not within .010" or so of being parallel I feel I need to do a little more homework...

Corwin

I am fairly new to wood working, but am an able machinist.  I really don't have a good feel for the tradeoff between accuracy and time in woodworking.  What can a good table saw do?  How important is it?

 

[John Stevens]

You are correct that I probably cannot be better than 1/32 across the length of the fixture using the rulers. Although, what I will probably do is use my combination square as a story stick from the working edge to the fence pointers, that should get me well beneath a sixty fourth...

I've been able to get multiple rips to about 1/64th with sticks, so I don't see why you won't be able to as well.  (I'm not a very talented or skilled woodworker.)  The necessary degree of accuracy depends on the project--I'm sure machinists take a similar approach.

A good table saw with a reasonably careful operator can make repeated rip cuts that are as close to perfectly parallel as necessary for any furniture or carpentry project with minimal setup time--seconds to set the fence, and maybe a minute or two to set up featherboards or similar safety aids.

Regards,

John

 

[Warrior]

Craig,
Nice job on the jig. How does it work with stock of varying thicknesses? It seems that you are pretty much limited to using stock the same thickness as the body of the jig unless you were to make up a bunch of shims. making the shims would be time consuming and storing them a pain.

Thanks,

Eiji Fuller

 

[mhch]

My 2 cent idea for thickness adjustement:  4 or 6 nuts epoxied within the wood and
a set of bolts, acting as height adjustable legs.  Adjustment is limited by
say half the thickness of the wood piece, hence the need for several
sets of bolts.

 

[enderw88]

Varying thickness is solved using Popsicle sticks.  I keep a box of a thousand around for stirring and various other uses, you can make shims pretty fast with titebond 3 and varying the number of shims.  The shims don't take much force, so five minutes of the glue drying is adequate.  But in general you are correct about varying thickness, especially thinner than the jig is. 

The principal goal for this jig was to let me cut the webs for a torsion box router table without spending a minuter or two truing up the stock for every piece, it worked very well for that.