Sliding deadman

[John Schroeder]

I'm building a roubo bench and have a question about the sliding deadman. i've got all the books (schwarz x 2 etc) and haven't found an answer, so I'm hoping someone that's done it can help me out. I'm going to route a 1" deep track underneath the top and cut a 45 degree bevel on the front stretcher. My question is: how do you get the deadman in the groove after the bench is assembled? the bevel i think will block inserting the top of the deadman, no? I get how it would work if you ripped the bevel off and put it back on with counter-sunk screws, but I'd rather not do that. On the other hand, I'd hate to have it all together and not be able to get the deadman installed. Likewise, if i just put it in when I assemble the base, i'm not sure how I could ever get it out. i guess i wouldn't really need to, but Chris schwarz put a bevel on one front stretcher as an insurance policy in case he wanted a deadman later. What I can't figure out is how he planned to get it into the track. Any help from someone that's been there done that would be much appreciated!

[Peter Cobb]

Works like aluminum windows: the groove in the benchtop is deeper than the tenon on the top of the deadman.
The shoulder on the deadman is lower than the benchtop. It allows you to lift it in and out over the the bevel on the stretcher.
The result is stable because the deadman supports the weight onto the bevel, but if you lift the deadman it will easily come off the stretcher.
If it doesn't make sense I can add a picture.
This image (http://correawoodworks.wordpress.com/2011/07/07/sliding-deadman/) is an extreme case with an added tenon on the back
This image of Jameel's Roubo (http://1.bp.blogspot.com/_NrLnumDfM90/SqQVmEDCMmI/AAAAAAAACQ8/EaMMMInkbOI/s320/jameelroubo3.jpg) shows how the deadman's tenon actually floats in the deeper mortise in the benchtop, with space for the benchdogs (sort of cranked out of the way)
Cheers,
Peter

[John Schroeder]

Thanks for the reply Peter. If the groove is 1" wide and the tenon is as well, or just slightly less so is slides easily, wouldn't that prevent it from being inserted as you'd have to angle is slightly in front or behind the bevel to insert the tenon? Does that make any sense? either way pics would be great, thanks!

[Peter Cobb]

You are right. The fit isn't that of a M&T joint, there's a bit of slack in it. In fact the slack needed to allow insertion means it doesn't bind when sliding and should permit removal of debris from the stretcher's bevel.
Hope the pics help.
Cheers,
Peter

[Roy Lindberry]

Think about it this way...

If your V groove on the bottom of the deadman is 1/2" tall, then you might make the slot in the benchtop a full inch deep, with a 1" tenon on the deadman. Then you would slide the tenon all the way up into the top groove, giving you 1/2" clearance over the bevel on the rail. Then when you drop the v notch onto the rail, it will drop down a 1/2", but the 1" tenon will still have 1/2" inside the top groove. This is, of course, assuming the overall dimension of the deadman is 1/2" shorter than the overall space for it.

This is a description of the process, but I just made up the measurements. Use whatever measurements will work well for you.

[John Schroeder]

Hi Roy,

That all makes sense, but you'd need a fair bit of slop to insert it, no? Using your example, when you go to insert the deadman, the bottom of it is even with the bottom of the bevel but has to be either in front or behind it. The top of the tenon clears the bottom of the bench, but to insert it you have to angle it slightly, as the bottom of the deadman is not yet sitting on the bevel and not at 90 degrees/perfectly vertical. How much thinner does the tenon need to be than the slot? if the slot is 1", then 7/8, or even 3/4? wouldn't either produce a loose fitting deadman that rattles in the track? Tell me if i'm way over thinking this. FYI I just finished assembling four huge handcut dovetails together to hold my two end-caps. much to my surprise they turned out pretty well so at this point I'm trying not to screw anything up. The front dt's are glued, the back not to allow for expansion on the tenons inside the endcaps. Looks pretty good, hope they stand the test of time. Pics attached, thanks again for the help.

[Peter Cobb]

I'm sure I saw a schematic in one of the "Woodworking Magazine" issues.
I'll try a hand at NeanderNet :D illustration : + benchtop, * deadman, I stretcher, . air

Really nice DTs on the endcap.

+++++++++++++++
+++++...+++++++ <--Benchtop
+++++**.+++++++
+++++**.+++++++
.....**........
.....*****.....
.....*****..... <--Deadman
.....*****.....
.....**.**.....
.....*III*.....
.....IIIII.....<-- Stretcher
.....IIIII.....

Cheers,
Peter

[Andrae Covington]

That all makes sense, but you'd need a fair bit of slop to insert it, no? Using your example, when you go to insert the deadman, the bottom of it is even with the bottom of the bevel but has to be either in front or behind it. The top of the tenon clears the bottom of the bench, but to insert it you have to angle it slightly, as the bottom of the deadman is not yet sitting on the bevel and not at 90 degrees/perfectly vertical. How much thinner does the tenon need to be than the slot? if the slot is 1", then 7/8, or even 3/4? wouldn't either produce a loose fitting deadman that rattles in the track? Tell me if i'm way over thinking this...

Hey, you're over thinking this.:D

It is a conundrum though, how do you angle the deadman to fit it into the groove in the top and clear the double bevel on the stretcher below. The angle required and length of tenon depends mostly on how close to the front of the bench the groove is. In Schwarz's first workbench book, the drawings show a 5/8" wide by 1-1/2" deep groove set 5/8" back from the front edge. If the groove is further from the front edge, and/or wider, that affects the geometry.

Wait, I think I'm over thinking this...:rolleyes:

At any rate, yes there will be slop. I don't think it's anything to worry about, and as Peter said, it keeps the deadman from binding as you slide it back and forth. Once you get it into position, all it has to do is hold a peg out in space to hold up one end of your workpiece. So maybe the peg (and deadman) ends up canting at some angle and doesn't meet the entire edge of your workpiece... big deal. Your vise will be doing most of the work, but with longer boards you may need the deadman peg to help resist the cantilevered weight of the board trying to pull the board out of the vise. The weight of the board on the peg should keep the deadman from wiggling around.

When building my Roubo, I decided a sliding deadman wasn't nearly complicated enough so I made a sliding leg vise. I based it on a Roubo illustration of what he called a "German" bench, and Jameel's original wooden-screw version of the same illustration. You can see mine in this tread (http://www.sawmillcreek.org/showthread.php?168360-Shop-made-Vise-designs&p=1730532#post1730532).

http://www.popularwoodworking.com/wp-content/uploads/2010/10/RouboGermanBench.jpg

Getting back to the deadman, something to point out in the Roubo illustration. Note that the lower guide track on the stretcher stops short on the left side. This is another approach to getting the deadman (or sliding leg vise in this case) on and off.

[Michael Peet]

Hi John,

It might also be helpful to bevel or ease the back edge of the sliding deadman's tenon. You want just enough to allow it to slip in when tilted to clear the front rail, but not enough to introduce a lot of slop in ordinary operation. Something like this:

201799

Just take your time and make lots of test fits until you get it.

Nice-looking dovetail, BTW.

Mike

[Paul Cahill]

Hi John,

It might also be helpful to bevel or ease the back edge of the sliding deadman's tenon. You want just enough to allow it to slip in when tilted to clear the front rail, but not enough to introduce a lot of slop in ordinary operation. Something like this:



What Mike sketched is exactly what I did:
201800

I only had to give the back of the tenon a very slight bevel to help it slip in. I made the grove slightly narrower than the tenon, and then used a block plane to sneak up on the fit. It is snug enough that the deadman will hang in up position when you first insert it (if you want it to), but as soon as you touch it it will drop down, and slide easily. Hope this helps.
Paul