Review the safety of this jig?

[cdolcourt]

Hi folks, 

I am helping a friend build a mantle clock using plans he purchased. Had we read the directions more carefully we would have seen that we should have cut a large rabbet in a long piece and then cut the pieces to length and then mitered to make the face frame in which the mechanism resides. But now we are in a situation where we need to hog off a large rabbet off a piece that is 1 3/4 inches wide, 5 5/8 inches long, and 3/4 inch thick. The resulting rabbet will leave the frame 1/4 inch thick by 3/16. Had we used one long piece I would feel much better about a dado stack or standard blades and make a small cut in and then the tall cut to free the waste. But with the position we are in, trying to raise the blade to 1 5/8 and then cut means very little to push and kickback seems inevitable. The attached image should clarify the cut. 

 

I have suggested a few options, including a hand saw to make a rip "stop" cut and then effectively rip the remaining waste to the line. Or we could chisel the waste, or combination. Or we could make a frame to hold the piece and second layer to act as a guide and run a pattern bit to cut the rabbet. But the other day I was wondering about making a plywood vise and turning the concept around so that we hold onto a plywood sandwich, and after making the first "stop" cut, then clamping between two pieces of plywood and using that to carry the piece across the blade. Again, diagram attached. 

 

My concerns are 1: safety of the concept. Will the blade pinch and cause kickback or something else? 2) if the idea is not bad, what about the offcut? Do we need to put a cleat at the back to push the offcut through? I do have a riving knife on the saw. Will the riving knife, if adjusted to be dead in line, be ok, or will it cause a problem?

 

Are there other, better approaches we should take rather than risk fingers, kickback, etc?

 

Thanks for your thoughts. 

 

[Tpt life]

I am not truly understanding all of the design concept but will offer one different thought. Unless you are building out of ebony, how much effort is this worth? Will it just be quicker and easier to make new parts? I ask this question more often after agonizing over many "fixes" that wasted my time.

[wtnhighlander]

I think C Shaffer hit the nail on the head. Unless the material is very difficult to replace, you are much better off starting over for a piece that small. Too many danger points to be worth the risk.

[cdolcourt]

I definitely understand what you're saying. It's soft maple, so the cost is not high. My friend wasn't big on repurchasing more and I don't think he has sufficient scraps to mill and cut the four pieces again. But sounds like that is the best approach.

To clarify, the first image is what we are trying to make out of a trapezoid. The pieces have been cut to length and then mitered, so the amount of material leftover to work with is not much. The second image I was trying to show how that piece would be secured between plywood and the cylinders are screws to hold the "vise" together. The horizontal and vertical lines in the piece are where the cuts need to be to cut out, what I may be incorrectly calling a rabbet. The remaining pieces would then be made into a frame for the clock face to sit in.

So the idea was to make the shallower horizontal cut first, then use the vise to hold the piece to make the deeper vertical cut, freeing the waste. But again as you said this may be a waste of time, effort, and overall not worth the risk of going and getting more stock.

Sent from my SM-G900T using Tapatalk

[wdwerker]

I would use 2 cuts with the tablesaw. I would put a 1/8 ( or 3/32 if using thin blades) piece in the first cut to keep things square when I made the second cut. The Grrripper push block should make it workable.

[weithman5]

I would use 2 cuts with the tablesaw. I would put a 1/8 ( or 3/32 if using thin blades) piece in the first cut to keep things square when I made the second cut. The Grrripper push block should make it workable.

This would work, as would by hand. But I think trying to build your plywood vise is more extra work than just getting a new piece to start with

[dwacker]

I would not balance cut the piece. All you need is an outfeed shoe and a push block. This is easy on either the router table or table saw. If you have a rabbeting jointer you may be able to use that. An outfeed shoe can be affixed with a dab of super glue or carpet tape. 

[cdolcourt]

I'm not familiar with an outfeed shoe (or perhaps I am and don't know the term). I don't have a jointer and use my router table with a straight bit to joint. I do have the gripper 3d, if that would work. Or I can make a sled and pushblock, if that's what you mean by outfeed shoe?

Sounds like there are several options on this. Man woodworkers are indecisive .

[dwacker]

An outfeed shoe in this case is nothing more than a scrap of wood in this case. On your router table make a scrap of wood the same size as your rabbet maybe a little longer. Stick it to the table just behind the cutter. As you feed the wood through the cutter the scrap will support the narrow edge and allow you to use the push devise without your work piece tipping into the cutter. You're doing the same thing as your split fence for jointing.

[cdolcourt]

Thanks. Sounds like I was over thinking and making this into a Rube Goldberg type problem. If I understand correctly all we need to do then is set the fence to the final dimension (1/2") and then raise the cutter incrementally to reach the final 3/16 ledge. At 1/4 inch per pass it would only take 7 passes per piece, which is not bad at all. The shoe would be a piece 1/2" thick by say 7 inches long and would effectively fill the void where the cut away wood was, effectively extending the fenc into that negative space. But we would only need that for the last couple of passes once that narrow edge gets thin, right, not for the first inch in bit height since there would still be 3/4 of wood left from the original 1 3/4" height.

That about right?

[dwacker]

Thanks. Sounds like I was over thinking and making this into a Rube Goldberg type problem. If I understand correctly all we need to do then is set the fence to the final dimension (1/2") and then raise the cutter incrementally to reach the final 3/16 ledge. At 1/4 inch per pass it would only take 7 passes per piece, which is not bad at all. The shoe would be a piece 1/2" thick by say 7 inches long and would effectively fill the void where the cut away wood was, effectively extending the fenc into that negative space. But we would only need that for the last couple of passes once that narrow edge gets thin, right, not for the first inch in bit height since there would still be 3/4 of wood left from the original 1 3/4" height.

That about right?

 

Lay it down. Your first cut would be a dado working from the inside out. Move the fence and take another cut widening the dado. When you get to the last cut is where you need the shoe since your knocking off one leg.

[cdolcourt]

Ah! Thank you all for your advice and thoughts. Very much appreciated. I'll let you know how it goes.

[cdolcourt]

Thanks for all the help. Yesterday we got the pieces routed safely and pretty oquickly using the shoe (or at least how I interpreted the description. Photo attached). The only issue we ran into is that we used a 3/8 inch straight bit with 1/4 inch shank, as we were concerned about routing the full 1/4 height (I was thinking 1/2 inch originally) with a 3/4 inch diameter straight bit- In other words routing a 1/4 x 3/4 groove - each pass. I use a musclechuck and used the 1/4 collet insert. The bit crept upward changing the depth of cut fairly substantially, but in a place that won't matter. Upon inspection, it looks like the collet insert migrated upward, not the bit itself. I've removed the musclechuck, cleaned it with some simple green, and replaced.

That brings up a question though: should collets be oiled at all? How do you prevent rust?

[chefmagnus@grics.net]

Nice Table. Pretty GRRiper.

[wtnhighlander]

I'll toss out the opinion that collets should be lightly coated with oil, just enough to help prevent rust. Dust may stick to it, but rusted collets are no joy...

[cdolcourt]

Thanks Chef! (reminds me of Southpark. I miss him). I built it to act as an outfeed for my lowered tables, and the lip in front allows me to clamp a dovetail jig, again to be about my height. I still need to add some drawers.

And thanks, wtnhighlander for the oil opinion. I was concerned about oiling something that is supposed to be grippy, but with appropriate force I suppose the oil will have a negligible effect on the strength. Salt Lake is usually pretty dry air, so that helps, too.