Adding Sacrificial Straight Surface to Table Saw Fence: What and How? - Woodworking Talk - Woodworkers Forum
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post #1 of 43 Old 06-02-2018, 02:10 PM Thread Starter
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Adding Sacrificial Straight Surface to Table Saw Fence: What and How?

High up on this weekend's suckat list (things I suck at doing) is adding some sacrificial straight and flat surfaces to my extruded aluminum table saw fence that has T slots already in it for doing just that.

The previous owner to my fence already added a sacrificial surface, but I find it deficient in three ways:

1. He put the mounting bolt precisely where the big bold instruction label still in tact on this 30 year old fence stated NOT to put a bolt... directly in the path of the saw blade. Automatic fail. Must be changed.

2. He used CDX plywood. Not exactly the smoothest surface to run boards along.

3. He only mounted a surface on one side of the fence. I want a surface on both sides of the fence.

4. He didn't make the sacrificial fence long enough to cover the base fence, which creates a catch point when introducing sheet material to the table. It also reduces the ability of the fence to keep the material aligned prior to being cut.

So this means a redo, and rather than limit myself to just correcting his mistakes, I thought to put post my intent on this wonderful board of woodworking talkers, in order to seek some advice to help me avoid making mistakes of my own. So please post your experiences, thoughts, recommendations, and past mistakes that you would do differently next time, on adding sacrificial surfaces to fences.

The first question I had was regarding materials.... UHW plastic, vs Baltic Birch Plywood, vs MDF, vs Yellow Pine, vs Melamine... I've read a smattering of recommendations for each, only to be faced with lack of local availablity of the most preferred materials. I still seek advice on the pros and cons of each type of material, but in the meantime, I'm going to make a practice run at this with MDF as an interim improvement over the CDX and nothing that I have now.

The second question I had was regarding elevation... how much higher than the original fence should the sacrificial fence extend above the factory fence?

Third question: Fence float... should the sacrificial fence extend no lower than the factory fence, in order to float easily across the table? Or should the factory fence extend a millimeter or two below the factory fence to practically an interference interface with the table, in order to prevent slivers from sliding underneath the fence?

The fourth question is hardware orientation. With T slots in the aluminum extrusion, should I slide square nuts into the extrusion slots, and mount bolts through the sacrificial fence surface, with the bolt heads recessed? Or should I slide the heads of short square headed bolts into the extrusion slots, and capture the sacrificial fence surface with nuts recessed into the material? Pros/cons of each? Is there yet another, better way to make the attachment? Different type of hardware altogether?

The final question is one that I haven't and cannot ask, because I don't know enough to think of it. But you might, so please ask and answer those unknown questions with regard to mounting sacrificial surfaces onto extruded aluminum fences.

It shouldn't much matter, but I happen to have an Exact-I-Rip fence with one T slot per side on the vertical surfaces of the fence, and two T slots on the top surface of the fence.

Thanks in advance for your assistance!


.

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post #2 of 43 Old 06-02-2018, 02:34 PM
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I have used MDF for decades as fence/sacrificial/sled type stuff - subject to the caveat that after cutting/building/construction/gluing/whatevering you put on a sealing coat of polyurethane.

MDF swells & warps with moisture - including humidity - but one coat of poly, heavy on the raw edges, prevents that. given the edge voids/etc in plywood, the MDF seals better imho - and drips/runs are rarely an issue as it sucks up the poly near instantly.

it stays straight & flat & smooth - it's inexpensive so if I need to chop/hack into it I don't hesitate or regret. other thoughts come to mind when considering sacrificing a nice chunk of 3/4 birch.....

as the need requires I use brads/nails/screws for stops/etc - a sharp chisel removes any bumps to the flat surface when you are done.

if you want something 'slicker' aka less friction look at the ready-made shelving. plastic coated for smoothness - but I still poly coat the edges to prevent any swelling with humidity. I use that for fencing on the router table where slick is good. here you can see the coating is torn a bit where a sharp edge caught - it's also cheap - about $1.50 for the piece so I'm not upset when it needs replacing . . .
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post #3 of 43 Old 06-02-2018, 02:41 PM
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I have three or four of those sacrificial fences. Not sure how I wound up with that many, but guess they serve their needs. Maybe one day Iwanted one and could not find what I had so just made another. Only takes a few minutes to make. One has a T track in it so that I can put feather boards on it. One is made of plywood and the other solid wood. Nothing special about any of them. Just whatever wood I had on hand when I wanted to make one.



Do not have any idea of a bolt you are talking about on yours. Mine have two bolts, one about 1/4 was in from each end. tThe nuts on the bolts are captured by the T track in the fence. The heads of the bolts are countersunk into the wood. They are bolted so that they just barely clear the top of the table.



Simple little items with minimal construction hassle. I have no need of a sacrificial board on the side away from the blade. Why would you want one?


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post #4 of 43 Old 06-02-2018, 02:51 PM
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My table saw also has has an extruded aluminum rip fence with T-slots on all three exposed faces of the rip fence (as well as the miter fence), and I have made several jigs and fixtures that utilize the slots. I made a tall fence add on that has faces on both sides of the fence and has small guides that slide in the side T-slots. The top of the tall fence has threaded inserts in it so that a pair of 1/4x20 bolts can be run down to bear on the top slot. The fence slides onto the rip fence and is so snug, I've never needed the bolts to secure it. This tall fence is made from hard maple scraps and also has threaded inserts in the faces to attach things like sacrificial faces. It was made double sided to use for panel raising. My saw is a right tilt saw, so I do panel raising with the fence on the left side of the blade. Normally the fence is positioned to the right of the blade for sawing and dadoing. I also have a tenoning guide that slides on the rip fence guided the the T-slots. It is made from some 3/4" quality plywood. I also made a router table fence that mounts on the top T-slot with some flat head bolts with fender washers that fit into the T-slot to secure it to the rip fence. The router fence is constructed from plywood also. All of these jigs were stained and varnished to help keep them fresh. The following articles have .pdf files attached that give the details of construction. I hope this gives you some answers to your questions. Apologies for the poor photography in these old articles. I didn't have access to Photoshop to clean them up back then.



https://www.sawdustzone.org/articles...-panel-raising
https://www.sawdustzone.org/articles...3000-tenon-jig
https://www.sawdustzone.org/articles...truction-notes
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post #5 of 43 Old 06-02-2018, 02:59 PM
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The shelving is Melamine

Melamine is nasty to work with because it's razor sharp. Other than that it's really slick and good for sliding contact from wood workpieces.
This is a miter gauge with T tracks and a sacrificial fence and would be similar to yours

There are other ways to attach your sacrificial fence like this:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #6 of 43 Old 06-02-2018, 03:44 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post

There are other ways to attach your sacrificial fence like this:

I was visualizing never removing the sacrificial surfaces (at least the vertical ones) and thus wanted to avoid using the clamp on jigs in your photo of the oak on the Align-A-Rip fence.


I was going to set my Zero markers on the fence to index to the surface of the sacrificial pieces that would be remain bolted to the fence permanently, much like what a Biesemeyer looks like (which appears as if built with a box beam of melamine laminated baltic birch plywood I assume, but do not know).
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post #7 of 43 Old 06-02-2018, 03:51 PM Thread Starter
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I have no need of a sacrificial board on the side away from the blade. Why would you want one?

Not sure... but my 30/24 fence has measured demarcations on both sides of the blade, and the fence has a continuous track that extends equidistantly away from either side of the blade, which indicates that it was designed to be used on either side of the blade, so why not protect it on either side of the blade?
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post #8 of 43 Old 06-02-2018, 04:06 PM Thread Starter
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Jim, I made a file folder in my computer with your name on it, and downloaded all three of your very detailed and helpful pdfs to it, and reviewed them. When I say review I mean that loosely... it was more like how a preschooler might review a PhD dissertation, recognizing a few words like "at" and "the", but not quite ready to grasp the concepts being conveyed. Even while recognizing the relationship of your three projects with what I'm trying to do, and readily seeing the advanced utility of the tooling you fabricated... all of that is going to have get added to my suckat list for a later time, after I've learned to walk.
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post #9 of 43 Old 06-02-2018, 04:13 PM
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make a slip on fence

Quote:
Originally Posted by Mad View Post
I was visualizing never removing the sacrificial surfaces (at least the vertical ones) and thus wanted to avoid using the clamp on jigs in your photo of the oak on the Align-A-Rip fence.


I was going to set my Zero markers on the fence to index to the surface of the sacrificial pieces that would be remain bolted to the fence permanently, much like what a Biesemeyer looks like (which appears as if built with a box beam of melamine laminated baltic birch plywood I assume, but do not know).
You need not attach your auxilary fence to your permanent fence, merely make it a snug fit so it comes off easily so you can turn it around if needed. This one has a higher side for certain operations:


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #10 of 43 Old 06-02-2018, 05:36 PM Thread Starter
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You need not attach your auxilary fence to your permanent fence, merely make it a snug fit so it comes off easily so you can turn it around if needed. This one has a higher side for certain operations:



But that's just it... I'm not trying to build the removable auxiliary fence (the wooden component in the photo above)... I'm trying to make and attach permanently mounted sacrificial sidewalls to my metal box beam fence (like the white walls attached to the metal box fence in the photo above).

Those white walls appear as if made with Delrin or UHW or some type of plastic... sacrificial, in that the white walls are replaceable less expensively than the metal box beam that makes up the spine of the fence itself.

Similarly, my metal box beam is an aluminum extrusion with T slots. As far as I'm concerned, it is made with unobtainium, since it is the spine to a fence that is forty years old and is not readily replaceable. I had to buy an entire saw just to get this fence. So I want to make sidewalls to protect the metal, exactly like the white walls shown in the photo above.

Then later on, I can graduate to building that drop on, reversible, instantly removable, truly sacrificial wooden fence that is shown hovering in mid air in the photo above, as well as the much fancier versions of the same as outlined in the pdfs of Jim Frye.

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post #11 of 43 Old 06-02-2018, 06:21 PM
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Quote:
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Not sure... but my 30/24 fence has measured demarcations on both sides of the blade, and the fence has a continuous track that extends equidistantly away from either side of the blade, which indicates that it was designed to be used on either side of the blade, so why not protect it on either side of the blade?

Why complicate a simple problem?


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post #12 of 43 Old 06-02-2018, 06:24 PM
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You need not attach your auxilary fence to your permanent fence, merely make it a snug fit so it comes off easily so you can turn it around if needed. This one has a higher side for certain operations:


What keeps it in position when the cutting blades are biting into it.



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post #13 of 43 Old 06-02-2018, 06:38 PM
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I donno?

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What keeps it in position when the cutting blades are biting into it.
George

Friction?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #14 of 43 Old 06-02-2018, 06:47 PM
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Mad: I purchased my table saw in 1993 and made those jigs within the first few years of ownership. I've always treated jigs and fixtures as regular woodworking projects. They are learning tools and that's why I fully finish them too. Well constructed jigs will last for decades and enhance your woodworking quality. The tall fence proved so useful that it has been permanently on the saw for the last 20 years. The router fence is mounted on a second rip fence for use with the table wing mounted router on the saw.
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post #15 of 43 Old 06-02-2018, 07:09 PM Thread Starter
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Why complicate a simple problem?

I just want my fence to look and function like the white fence in the photo above, where wood blade friendly materials are on both sides of the metal spine of the fence.

Since there are a variety of blade friendly materials that can be used, and an infinite number of heights above the fence spine that these materials could be ripped to, and a variety of ways the hardware can be oriented to accomplish the attachment... I thought it would be good to ask the opinions of those with more experience than I have in modifying or enhancing a fence.

It may be a simple problem for you, and that is great. For you.

For me, since I have not done this before, some questions occurred to me, such as those that I outlined in the original post. Questions like hardware, because if I use MDF, and I have to clearance a port for the hardware well deep enough so that the hardware recesses below the surface of the fence wall, then the strength and integrity of the material remaining beneath the point of attachment is naturally much weaker, and could potentially lead to rapid tearout when subjected to rapid forces transferring from a blade bind acting on the material being cut that is trapped against the sacrificial fence surface. So that possibility, about which I do not have the experience to estimate the probability of, led me to question either the choice of material, or the choice of hardware, or the orientation of the hardware, to reduce the risk, if the risk exists.

Yes, that does "complicate" the problem, but I'd rather ask and learn, than be soured into silence by criticism for asking the questions.


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post #16 of 43 Old 06-02-2018, 07:37 PM
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methinks you are over thinking the problem.


first - there should never be any blade biting. the sacrificial fence idea is to allow the blade to go past the vertical line of the (metal) fence. when you're going to be doing that you position the fence and gently raise the saw to cut a clear "pocket" first.



trapping a work piece between the blade and fence is not common except for really short (cross) cuts. if you are pushing a board thru on a rip cut and it binds up you need to immediately stop and figure out why. that is not normal and the danger is the harder you push the more apt you are to slip and rip something other than the wood - like your hand/fingers.


the fence should not just 'sit' unconstrained over the original fence. there should be something that pinches or grips or tightens to keep the sacrificial fence in place. the detail depends on your design.



using 3/4 thickness the remaining material under a 1/4-20 flat head bolt - or carriage bolt - or hex head bolt is more than adequate to not 'rip out'
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post #17 of 43 Old 06-02-2018, 07:53 PM
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Attaching a sacrificial fence ....

Your stock fence has T slots, so T nuts seem a logical way to attach any separate side panels or integral fence slip over design.... if needed.
In the automotive design field, we would speak about having bumpers on your bumpers ala 1960 Cadillac front nose cones. This reminds me somewhat of that since I am understanding you want to have side panels and then possibly and additional slip over piece?

I would simplify it to one or the other. UHMW plastic is not cheap:
https://www.ebay.com/itm/UHMW-Polyet...QAAOSwNvxa6IvE

Melamine is cheap and readily available. Hardwood is also cheap and available. Baltic Birch seem like a waste of good plywood, but it would look great and be flat. You can use flat head screws set below the surface, out of the way of the saw kerf, into T nuts in your existing fence. That's as complicated as I would get.
I personally like the slip over design with a friction fit, easy on easy of to flip around, but that's just my simple mind at work.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #18 of 43 Old 06-03-2018, 01:01 AM Thread Starter
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I have not been able to find any sort of "T Nut" that will fit.

The throat width to these T slots will just fit a 1/4" diameter bolt, and the throat depth will just barely accommodate the head of a normal 1/4 x 20 bolt, or the thickness of a 1/4 x 20 nut.

On the other hand, 1/4 x 20 T nuts designed for T slots have a require a wider width through the throat of the T slot, and a deeper depth in the channel of the T slot.

Most searches for T nuts yield the kind of T nuts that are round with tines for placement into wood, so you better believe I searched out machine tooling websites and looked at the dimensional specs for true T nuts before arriving at the conclusion that they may not be available for T slots this small.
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post #19 of 43 Old 06-03-2018, 01:06 AM Thread Starter
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Quote:
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the sacrificial fence idea is to allow the blade to go past the vertical line of the (metal) fence. when you're going to be doing that you position the fence and gently raise the saw to cut a clear "pocket" first.

What type of cuts or operations benefit from a blade pocket scarfed into a sacrificial fence?


Jim Frye's Cadillac bumper on top of a bumper secondary sacrificial fence also has a blade pocket (second photo in his high fence article/design).


What is the purpose of this type of fence where the blade is nested inside of it?


.

Last edited by Mad; 06-03-2018 at 01:16 AM. Reason: To rope in Jim Frye's design into TomCT2's declaration on the purpose of sacrificial table saw fences
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post #20 of 43 Old 06-03-2018, 01:26 AM Thread Starter
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Quote:
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Mad: I purchased my table saw in 1993 and made those jigs within the first few years of ownership. I've always treated jigs and fixtures as regular woodworking projects. They are learning tools and that's why I fully finish them too. Well constructed jigs will last for decades and enhance your woodworking quality. The tall fence proved so useful that it has been permanently on the saw for the last 20 years. The router fence is mounted on a second rip fence for use with the table wing mounted router on the saw.

I'm not dismissing your design and ideas. I was just admitting that it was going to take me a while to understand them. But I'm working on that understanding with every re-read. I see why you interjected... if I use the T slots on the vertical wall to bolt on a semi permanent side surface, then I lose out on the opportunity that you capitalized on, which is to use those T slots as retention guides for a slip on fence instead. Only rather than slipping on via downward application, your design slips on from the rear end of the fence in a reverse telescoping motion.

Once I bolt a semi permanent smooth faced semi permanently mounted sacrifical surface to the vertical sides of my metal fence spine, then I lose the use of those T slots as guidance rails. Yes, I'm starting to understand now. But I never claimed to be quick witted. If intelligence is a prerequisite for posting questions on this forum, then I am woefully underqualified. So I do appreciate everyone's patience as I try to catch up and learn something here.
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