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Discussion Starter · #1 · (Edited)
I watched this video (and many others) and this seemed reasonable and easy so I thought I would build it.
In the below picture, highlighted in blue is my base which is 1/4" thick, three layers, birch plywood (relatively flat)
On top of it I have an 11 layers piece of Baltic Pywood (3/4") and two Bessey STC HH70 toggle clamps . The clamps are an overkill for this sled but they are there on a temporary basis I can remove them and use them where I need (they are installed using insert screws)

To me this design has a flaw and that is that if you are using a thin base (to avoid having to lift the bit too much) the clamps will push the base downward and the base will bend or the base will be pushed upward putting pressure on the screws that connect the base of the sled (blue) to the base of the clamps (purple)



Should the base be much thicker ? I did try to adjust the pressure the clamps put on the piece of wood in order to avoid the base bending but it ends up with the wood that you are routing getting lose

My sled is longer but that is because later I plan to get it up to this design

 

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Discussion Starter · #2 ·
also the design in the second picture seems to have an issue as well. It seems that the acrylic screen/cover is used to run the sled against the fence. The piece to be routed is sticking out of the base and it has no back support (unless a sacrificial piece is used).
I am considering the below design in which the side of the sled situated next to the fence and ahead of the purple
clamp base (yellow block) is cut in such away that would not allow the bit to reach the base of the sled because there is nothing there
(that yellow block was cut out)
 

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also the design in the second picture seems to have an issue as well. It seems that the acrylic screen/cover is used to run the sled against the fence. The piece to be routed is sticking out of the base and it has no back support (unless a sacrificial piece is used).
I am considering the below design in which the side of the sled situated next to the fence and ahead of the purple
clamp base (yellow block) is cut in such away that would not allow the bit to reach the base of the sled because there is nothing there
(that yellow block was cut out)
Is this router coping sled design OK ?
NO REALLY! Sorry.
In my new routing table which I am designing, there will be 2 parallel mitre slots (both with T-slots). So the runners will only have a cross-piece for hold down clamps. There will be no need of MDF nor Acrylic nor plywood or any sled of any thickness since the workpiece will be supported by the 2 mitre track runners which will be made the same level as the router table top itself.

(I bought 2 Aluminum Mitre Tracks to be precisely embedded in 2 precise parallel DADOS of correct depths to be routed out by my small CMC router.
My table top will be 38mm thick Free of Charge "sink cut-out" of a post-form kitchen worktop laminate).
 

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No really
So what is wrong with it...
If I am stuck with that router table, I would buy a ER20 collet extension so that I can place a stationary piece of wood of same thinkness as a thicker sled - with a round hole of almost zero clearance and put over the router bit. Safety and work. quality

(main reason why I want a new router table - read my comment #3 again)

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Discussion Starter · #6 ·
So the two problems I am seeing are real, itis not my imagination.
#1 the router base needs to be thin in order to not to have to lift the bit too high
#2 using those toggle clamps is not a great idea since they tend to push the thin base away from them and since this is thin it will bend.

Two contradictory requirements

I looked at that bit extension and a good one could be quite expensive. Besides that you need two sizes 1/2 and 1/4
 

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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.
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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.
 

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I looked at that bit extension and a good one could be quite expensive. Besides that you need two sizes 1/2 and 1/4
I paid about USD30 for a good one from UK bundled with 1/2", 1/4", 1/8" collets.
I also bought a cheap 13 pieces ER20 metric collet set 1mm to 13mm (made in China) for another USD20

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With an ER20 collect extender, I could use CHEAP router bits (shank dimension precision becomes irrelevant) and I also need not remove the 2 column strings from my plunge router. Easy to change bits above the table. My sled could be nominal 3/4" plywood. (Actually, only 18mm now in Australia)
 

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Screw the thin piece to the top from underneath so you can replace it should it bend. The only time you are applying pressure with the clamps is when you have clamped a piece in place. Quarter inch BB ply should work fine, and is expendable

If your stile is narrow, you will want to be able to clamp another piece in front of it, with your clamp on, or spanning both the first and second piece.

I don't much care for coping sleds and learned to just use a square piece of MDF cut nice and square. I hold the workpiece in place with my hands, which is adequate since the end is also running against the fence,so it is automatically positioned correctly. If not, make a second pass.. The push block will be chewed up for an inch or so past the corner because I run it against the fence. Don't want to change the fence position or bit height between rails and stiles. I do use matched bit sets, so changing height defeats the point of matched sets.

Check out some of Marc Sommrfeld's technique. He doesn't use a coping sled and it's how I learned to use simpler methods.

If you are using matched sets, drop a grommet (not an O ring) into the collet so the bits bottom out at the same depth. I use only matched sets..
 

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But nobody use 1/4" cross-cut sleds for their table saw. It's almost always 3/4" (now 18mm).
But a coping sled has a completely different purpose and requirements. If 1/4 raises the bit by that much, the 3/4 ply will require an extension, which the OP wasn't eager to pay for. It is a replaceable part of a shop made jig. BB is unlikely to bend, while cheapo Chinese ply might. Again, the only time clamping pressure is applied is when it is in use, and then it's supported somewhat by the table itself.
 

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Discussion Starter · #18 ·
I went to Ikea this morning and I noticed they have various trays and cutting boards made of bamboo.
In particular the one below could be used (the slotted piece) -cost is 12-13CAD, the thickness is a little bit over 1/4"

 

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Discussion Starter · #19 ·
Here is how much I can lift my router - do you think I can/should go with a nominal 1/4 or 5/8 or even 1/2 plywood for the base of the coping jig? Would I still need an extension bit?
 

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Here is how much I can lift my router - do you think I can/should go with a nominal 1/4 or 5/8 or even 1/2 plywood for the base of the coping jig? Would I still need an extension bit?
Go for 1/2" plywood sled. Hard wood workpieces are NOT cheap.
Collet extension need not be bought immediately.
I bought mine from Axminster UK (Made in the UK)
It is cheaper than the "muscle chuck" and in the long run I saved a lot on router bits because ER20 collets DO NOT need router bits with precise shanks diameters available from only a very few expensive router bit makers. An 1/2" ER20 collet will perfectly mount a 12mm shank bit and a 1/4" ER20 collet will mount a 6mm bit perfectly too. You will never hear of ER20 collets getting stuck in the shaft and people asking for help in ROUTER FORUMS.
 
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