overhead or under table routing?

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lew
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overhead or under table routing?

Post by lew »

I have a standalone OPR, the one with the option for a traditional under table router. I've mostly use the overhead position as a mortiser of sorts and have done some very limited pinrouting, bat templates for a bat house.

Anyhow, I am getting ready to make some Adirondack chairs and anticipating some pattern routing in my future. Curious as to what situations it makes sense to use overhead vs. under table, or if it's mostly a matter of preference.

--Lew
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BuckeyeDennis
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Re: overhead or under table routing?

Post by BuckeyeDennis »

lew wrote: Tue May 31, 2022 12:29 pm I have a standalone OPR, the one with the option for a traditional under table router. I've mostly use the overhead position as a mortiser of sorts and have done some very limited pinrouting, bat templates for a bat house.

Anyhow, I am getting ready to make some Adirondack chairs and anticipating some pattern routing in my future. Curious as to what situations it makes sense to use overhead vs. under table, or if it's mostly a matter of preference.

--Lew
I also have a standalone OPR. Mine is equipped with an undertable router (the 3-1/4 hp Triton) and a nice Jessem fence. If you're interested, all the gory details can be found in this thread.

I use the undertable router more than I do the overarm router. But for operations that require a lot of in-and-out plunging, such as mortising and pattern routing, I wouldn't even consider using the undertable router. Except maybe to hold a guide pin.

The plunging features of the overarm are far superior to any undertable system I've ever seen.
  • Fast lever actuation of the router plunge, easily offset to place the lever in a comfortable position
  • Fast plunge locking, by simply twisting the plunge lever
  • An independent micro-adjustable plunge stop, for consistent blind-pocket depths
I use the built-in features of my Triton as a poor man's router lift, and it certainly can't do all that stuff. I'm not sure that even the high-end router lifts have independent plunge stops, and I'd bet that their height-adjustment mechanisms will be occluded by the pattern/carrier.

One more feature that would be nice to have on the OPR is a multi-step plunge-stop turret, like the ones on modern plunge-router bases. It would probably a fairly easy modification to transplant one onto the router arm, come to think of it. Failing that, you could hold a setup block beneath the stop screw with your other hand while plunging to an intermediate depth. But then what would hold the workpiece while you're plunging into it?
lew
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Re: overhead or under table routing?

Post by lew »

Thank you. Your thread is what convinced me to buy the OPR when I saw one listed on craigslist a few years ago. I picked up the Jessem fence, but haven't made the other modifications yet.
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reible
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Re: overhead or under table routing?

Post by reible »

The major difference in above vs below routing may not be as apparent as it first seems. The fundamental different has to do with the bit to reference surface.

Where a below operation has the bit coming from the same reference surface to the cut the above version the bit is coming from the non reference surface.

So a simple example is if you want to cut a groove in the below example the distance the bit sits above the reference surface, ie table top, is the depth of cut even if the material being cut is not the same thickness. If you reverse this and have the bit coming in the opposite direction the distance between the bit and the table is the constant.

Say you have a bit set at a depth on the below situation, you can pass any thickness of material over the bit and the cut remains the same depth. If you do that with the bit above this is not the case. Passing a 3/4" work piece thru will result in a different depth of cut then if you pass a 1" piece thru.

Hope this makes sense. I have a post here somewhere with drawings and more but I can't find it now.

Ed
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BuckeyeDennis
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Re: overhead or under table routing?

Post by BuckeyeDennis »

reible wrote: Tue May 31, 2022 11:12 pm The major difference in above vs below routing may not be as apparent as it first seems. The fundamental different has to do with the bit to reference surface.

Where a below operation has the bit coming from the same reference surface to the cut the above version the bit is coming from the non reference surface.

So a simple example is if you want to cut a groove in the below example the distance the bit sits above the reference surface, ie table top, is the depth of cut even if the material being cut is not the same thickness. If you reverse this and have the bit coming in the opposite direction the distance between the bit and the table is the constant.

Say you have a bit set at a depth on the below situation, you can pass any thickness of material over the bit and the cut remains the same depth. If you do that with the bit above this is not the case. Passing a 3/4" work piece thru will result in a different depth of cut then if you pass a 1" piece thru.

Hope this makes sense. I have a post here somewhere with drawings and more but I can't find it now.

Ed
All true, and it makes perfect sense. But I can think of at least one example where a constant depth of cut isn't the objective. Suppose that I'm hollowing out router bowls (or snack trays, etc.) with a bowl bit, and I want the bottom thickness to be 3/8". If I pattern route with the overarm router and a fixed depth stop, I'll get a 3/8" bottom thickness on any bowl, regardless of the blank thickness.

But even when the objective is to get a constant depth of cut, I'd argue that it's a simple matter to reference the overarm depth stop to the top surface of the workpiece. Just lower the router until the bit touches the blank, and lock it in place. Now adjust the depth stop until it just touches a gauge of thickness equal to the desired pocket depth, and lock it down. Done.
Hobbyman2
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Re: overhead or under table routing?

Post by Hobbyman2 »

I dont have a OPR but can you not use one as a planer, or to flatten / true a board ?
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BuckeyeDennis
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Re: overhead or under table routing?

Post by BuckeyeDennis »

Hobbyman2 wrote: Wed Jun 01, 2022 9:55 am I dont have a OPR but can you not use one as a planer, or to flatten / true a board ?
I've never done it, but I don't see why not. You'd just need to mount the workpiece on a sled that slides on the OPR table. The cutting passes could be very well controlled if you adjusted the fence for each pass, probably by about 1/2 of the router bit diameter.

That would be similar to using a rotary planer on a Mark V in drill-press mode, which I have done. And boy, was it messy!
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