Building my new miter sled, pics and question

[cgallery]

I've included a pic of my original sled. It uses two t-slots and aluminum sub-fences that allow me to achieve any desired angle. I use a protractor to set the angles (nothing marked on the board).

It works great, with the only caveat being that it takes quite a while to adjust to an angle because I have to slide the sacrificial fence on the sub-fence. There are six knobs required for all of this. So, time intensive. Also, using a protractor each time gets tedious. Oh, and my kids keep taking my protractors for their homework!

I decided having something similar to the Dubby made sense (http://www.in-lineindustries.com/single_dubby.html). Rockler sells one of these, too. But $200 is too much to spend. But, I'd be able to make some permanent marks for angles, make fast adjustments, etc.

I decided to use an Incra 18" runner, and I made my substrate 17" square. This is a prototype, so I may go larger if I decide to make another one.

Instead of routing a slot for a carriage bolt (which would require removing my one and only router from my router table), I decided I'd use a t-bolt and t-slot. This clever (IIMSSM) alternative allows me to route the t-slot all the way to the edge of the board w/o compromising the strength of the substrate. I used a jig screwed to my router table's lift as shown in one of the photos. I use a 12" radius.

The only thing I'm kinda stuck on, and this is where you come in, is how to handle the pivot. I have a 1/4" hole that I used as the pivot to route my arc, and that will act as the pivot for my fence, too.

I could use a carriage-head bolt from underneath (which would have to be countersunk) into a knob above, but my substrate is only 1/2" thick (with the countersink this may not be thick enough to accommodate the square portion of the carriage-head bolt.

I could use a threaded insert in the substrate, but I SUCK at putting them in (and my experience is that they don't like plywood, they separate the plys).

I could countersink the hole from underneath and use a flat-head screw from the bottom into a knob on top, but when tightening from above the screw would spin in the hole underneath (nothing to grab it).

I have seen on McMaster a flat-head screw that had little bumps or keys in it that would prevent it from spinning in a hole. But I can't find them now. I can't remember what they were called. And I have never used them so I don't know how well they work.

I'm open to other suggestions, too.

[LCHIEN]

the flat head is the worst idea for the reasons you mention, even one with bumps.

The carriage bolt would work but a threaded insert or even T-nut would be the best, there's plenty of meat in a 1/2" for a countersunk carriage bolt or a t-nut.

[RickLab]

I think a threaded insert would be the way to go here. You say you suck at putting them in - do you mean hammering them in so they don't split the wood? If so drill some small holes where the prongs will go to get them started.I think you're missing the real issue here though and that is that you clearly don't have enough routers. I say that jokingly, but if you're talking yourself out of doing things because your router is too much of PITA to remove from your table, well then maybe it's something to keep in mind. BTW, nice progress so far!

[gearbuilder]

I'm thinking the inserts that split the wood were the ones that are threaded on the outside. The inserts with the prongs would probably work. IMHO

Jamie

[Sid]

What about just putting a 1/4" rod in the hole with epoxy, and protruding through the top of the substrate as the pivot?

Sid

[cgallery]

What about just putting a 1/4" rod in the hole with epoxy, and protruding through the top of the substrate as the pivot?

Sid

Sid-I'd like to be able to tighten the pivot point, too.

Loring-I found the name of the machine screw I was thinking of, it is called a "plow bolt." They have one with a large key that would prevent it from turning. They make another that is just like a carriage head bolt but has a flat, countersunk head. Problem is they start at 3/8" in size. So I'm probably back to countersinking a standard carriage head screw.

Ricklab-I was talking the threaded brass inserts. I could also use a t-nut, but I've had problems w/ the prongs bending on those, too.

Jamie-Not sure if you're talking about t-nuts or barbed inserts. I could try a barbed insert but I think they are > .5 long. I have some in the basement, I will check them.

A 1/4-20 or 5/16-18 plow bolt would be ideal, but if McMaster and Fastenal don't have them, I think I'm outa luck.

[gearbuilder]

The mcmaster carr number for what I was talking about is "90973A029". They call them tee nuts. I thought they should have been called prong fastners.

Still learning every day.

Jamie

[pecker]

Why can't you just use another T-bolt for the pivot. The oblong head on them is only about an 1/8" thick. I'm sure you could chisel out a recess on the bottom of the sled for it to fit into. Or create a proper mortise for it with that router if you'd take it out of the table for a moment.

[JR]

A flat-head screw could still prove useful. Fix it in place with 5-minute epoxy. The epoxy can then be filed flush and sanded smooth.

My router fence is made this way.

JR

[cgallery]

Why can't you just use another T-bolt for the pivot. The oblong head on them is only about an 1/8" thick. I'm sure you could chisel out a recess on the bottom of the sled for it to fit into. Or create a proper mortise for it with that router if you'd take it out of the table for a moment.

Yep, I'll use the same router bit used for making the t-slot grove, but use it from the bottom so the screw hole can still act as the pivot.

[JimD]

When putting in the threaded, typically brass although I use brass plated steel too, inserts, the size of the hole helps to determine splitting and how much the wood bulges due to the insertion of the insert. If it is critical, I try it first in scrap.

In terms of the acutal insertion, I am too cheap to buy the special T-wrench for this purpose so I just use a bolt with a nut I can tighten against the insert. I leave an inch or so of the bolt sticking out to help align the insert with the hole. I then crank it in with a socket or sometimes a wrench (socket tends to work better because you can push down on the insert). If I have to go to an oversized hole to prevent splitting, I set the insert in epoxy.

When I want a T-headed bolt, I normally use a scrap piece of 1/8 mild steel, tap threads for some all-threaded rod and braze them together. The brazing takes off any plating on the all-thread so it may not be pretty when you are done but the resultant bolt works fine.

Jim