[Ola C]

Correct observation, toogle clamps puts a lot of torque between the parts and needs thick bases not to bend them. They are also somewhat fiddly to adjust in height and to some extent length.

So, I almost always use routed in clamps instead. Rail clamps or microjigs dovetail clamps. Super quick to adjust in height and length and creates no bending load between the parts, that force is instead taken up within the clamp itself.

I have used rail clamps like the one in tje pics in 12mm baltic birch with good results.

Some pics of my very basic coping sled.

 

[Ola C]

Your base is not thin either -are you using a bit extender ?

Sometimes, if needed I do. My router travels quite far out from the base, that's also a factor.

If you want to go thinner you will need a metal or phenolic base.

 

[Ola C]

You who are saying 1/4" plywood will withstand toggle clamp force. Have you checked your base straightness after clamping a piece down? My old coping sled was 1/2" mdf and it couldn't take the slightest toggle clamp force without bending.

 

[Ola C]

Mine works fine. Not sure what you’re doing wrong? I made cabinet doors for manual years without any problems.

So yes, I’m one who does not have a problem using 1/4..

Ok, I see now you are running it in the miter channel and have a miter runner on the bottom side of the base pretty much located where the toggle clamp is(?). That runner stiffens up the base considerably if that is the case.

 

[Ola C]

You’re only holding the part enough to eliminate vibration and secure the part. It doesn’t have to have a death grip..

If I use clamps or hold downs I want them to hold the workpiece more firm than what is possible using toggle clamps onto 1/4" mdf without bending it.

 

[Ola C]

I am going to try 1/4" MDF first to see if that removes the bending I am seeing

No need to try, it will bend. Check this review (link in end of post) of different commercial coping sleds and their comments about if it bends under load. Just as I mentioned earlier they also see bending problems with 1/2" mdf, twice the thickness of 1/4". Phenolic or aluminium is your base material if you want to go thin, but even with those materials there is no commercial sled made as thin as 1/4". Router-Table Accessories

 

[Ola C]

Your guessing. I show pictures because it’s a fact. Not a guess. i don’t know what your doing wrong.

I think you way over clamp..

Guessing? You show pictures of your jigs, says absolutely nothing. Either you use super low toogle clamp force to an extent where the clamp is almost meaningless, or you have bent your jigs your entire life without noticing. The article I linked to see exactly the same problem with thin bases as I and the thread starter do, quote "but the 5⁄16"-thick acrylic base bowed until we reduced the clamping force to an almost uncomfortable level".

Quote#2 "its 1⁄2"-thick melamine-coated MDF base bowed slightly when clamping workpieces."

 

[Ola C]

I would recommend not using a runner even if it improves the bending issue.

Reason 1. If you use fence as length reference this needs to be absolutely parallell to the miter slot. That will be extremely annoying trying to dial in every time for each setting.

Reason 2. If you not use the fence as length reference you will have no support in that direction when you make the cut. You can put a block on the fence before the cut for length reference, but you will have no fence support during the actual cut.

Btw. Check with a straight edge on the backside of the base if it bends, a short pencil line on the fence is not much of a reference for measuring this.

 

[Ola C]

I would always have a runner for this application..

For what reason?

 

[Ola C]

Guarantees the part is against the cutter.

Jig does all the work…

How do you ensure the length position of the workpiece?

 

[Ola C]

Bump it against the fence

What are you trying run?

Ok, so then you always make sure the fence is parallell to the miter track?

 

[Ola C]

No different than a table saw fence, blade and miter slot.,

Big difference. A router fence doesn't need to be parallell to the cutter (it can't be parallell to a round shape) and very seldom travels parallell to a miter slot since it complicates the guiding of the fence considerably. I wouldn't make a coping sled that requires the fence to be absolutely parallell to the miter slot at all settings. On the table saw you will get away with the miter slot not 100% parallell to the fence since you never use both at the same time to guide the workpiece. Here you won't get away with that, they need to be spot on parallell if you use both in this operation.

 

[Ola C]

#1….. I use both fence and slot along with fence on the the table saw for tenons.
#2…You treat the router table or shaper the same.
#3… This is why we have Forman’s/ lead mans in place to keep things setup correctly and safe ..l
its your shop, do as you please..

OK, some people cut tenons like that I agree, but on a table saw you have a system for setting the fence parallell to the miter slot, on a router table you most often haven't.

....and most people don't have a foreman setting up their machines for a cut. It's not my shop we are discussing here, I'm trying to come with good tips to @MiniMe

Still consider a coping sled that requires parallellity between fence and miter channel a non preferred solution if you don't already have a system where these two automatically travels perfectly parallell to each other.

 

[Ola C]

Setting the fence parallel with the miter slot is not a problem, actually the jig helps with that, if I push the fence against the jig I know it will sit parallel with the miter slot and the fence line will traverse the center of the bit.

That's only for one fence setting. Sometimes it needs to be further back, sometimes further front. It's enough to change bit and use one with slightly different bearing diameter (if using these kind of bits which is quite common for coping sled operstions) to having to move the fence. Can be done using shims or other method but it complicates things a lot having to align the fence parallell to the miter slot.

 

[Ola C]

True and I agree
I was just looking at the mechanics of a fence adjuster from the back side.
There has to be one like the below one that adjusts both sides in sync.
This might not work for my Bosch router table as it has slots not channel slots

Yes, my fence for instance, video below. You should search for router fence micro adjust to get relevant hits and this is what you imo need to run the coping sled with a miter bar without too much hazzle.