Author Topic: krenov style sawhorses : mistakes were made  (Read 435 times)

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Offline mrFinpgh

  • Posts: 409
krenov style sawhorses : mistakes were made
« on: August 03, 2020, 10:59 PM »
I've wanted to make a pair of these for a while.  I don't really need them, but I have always been drawn to the design and thought it would be a good opportunity to experiment with using some new-to-me techniques as well as trying a couple finishes out.  I made a good number of mistakes along the way but they are still decent and the whole process was valuable.

The design on these is a basic trestle style, with a notched joint at the top to hold a replaceable upper part.  The joinery is mostly mortise and tenon, some hidden and some through with wedges.  I made them out of some ash i had picked up earlier this summer.

After some work to get a good face and edge, I ran everything through my planer to take it to final dimensions.  I stood the parts on edge with lots of airflow around everything.  My bench is a mess.

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Not captured here was the minor tedium of shooting the ends of every board w/ my plane. While I'm not trying to do an all handtool project, I don't really trust my miter saw at the moment and it's too noisy/dusty in the basement anyways.  So some quality time spent w/ my low angle jack plane, shooting board, and the occasional stop to resharpen.

I've never done a mortise with a router before, so this was new to me. I used my OF1400 with the edge guide and a whiteside upcut bit.  This bit was excellent and the dust collection was superb. I had built a small jig to create positive stops for the router, but I didn't account for the vacuum hose hitting it first.  Since I didn't have the materials at hand, I just routed to the lines by eye. Another first for me.  It went fine - perhaps 1/2 a mm over the line at most.

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Next up was the tenons. I don't particularly enjoy cutting tenons by hand, as I don't have a proper tenon saw.  My setup is a moxon vice and a veritas 14ppi dovetail saw. I recently filed it, so it was sharp, but ripping through 2.25" of ash is still not a great time. I mostly cut to the line, but there's always some cleanup to do and I think I may have been conservative w/ the marking gauge - they were all a bit fat.  In one case, my chisel must have gone with the grain, as I ended up paring in about .06" too much on the side of one tenon cheek. I had some veneer on hand, so I built the cheek back up. 

 I also erred by being a bit too conservative with my tenon shoulders. I really should have made a deeper knife wall and just cut to the line. I wanted to avoid my crosscut saw chewing the shoulder with it's teeth, but a deeper knife wall would have mitigated that, and made the shoulder line more defined. Cleaning up shoulders with a chisel is a hassle, and I inevitably end up bruising the shoulder line somewhere. 

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You can't see it well, but there's 2 layers of veneer being glued to the cheek, covered by wax paper, covered by some cork shelf liner, and then a piece of pine to distribute the pressure.

Some of the joints were a bit too tight. I didn't realize it at first, as they went together without a mallet and a bit of wiggling.  I erred on the side of tightness because most of the time these joints end up a little looser than they should be when I cut them.  I realize they were a bit too tight when I noticed the outside of one of the mortises bulging out slightly when the joint was together.  I'm reasonably sure that's too tight.   Some time with a rasp got me to a place where the joints went together firmly but no bulging... at least for now.

After all the joinery was done, I did some shaping with my very low quality bandsaw and my very high quality block plane.  I am really looking forward to the day I can accommodate a nice bandsaw in my shop (or having a real shop, for that matter).  Everything sanded to 150. I used the pro5 with 120 where I could get away with it, and then a mirka sanding block connected to a vac with some 150 abranet.  I have some suspicions that the abranet might be at the end of it's useful life, which is a bit of a concern since I'm going to be using Rubio color oil for these, and that tends to be very dependent on consistent sanding.

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Yes, there is a bit of chipout on one of the feet. 

A test fit:

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Not bad..  the through mortise looks pretty decent too:

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Lastly, during glueup.  This  glue up went well for the most part.  Clamping the legs was easy enough - one clamp per foot/leg.  I was able to almost completely avoid squeeze out by applying glue to the mortise walls completely, and only the first half of the tenon cheeks.  However,  a couple of my tenons definitely needed persuasion once the glue was one - they weren't going to seat completely with a clamp applying pressure.  What I noticed after is that the bulging I mentioned earlier returned - so the side wall of the mortise on two of the feet is under some stress.  I don't know whether this is going to be a blowout waiting to happen, or if the wood will eventually just .. conform..  we're talking about maybe a few thousandths of an inch, but it is noticeable if you run your finger over the outside face of the foot.  I also dont know whether that tight of a fit means the glue joint ended up starved.  I doubt it, my tenon cheeks are not that smooth.   :-)

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It might be clear here, but the one wall of the mortise is just slightly thinner than the other.  Not much, but apparently enough. 

I didn't capture it, but I definitely had some tough luck with wedging the tenons.  Most of them didn't drive in very far, and a number of them snapped while I was tapping them in.  I have done wedged tenons before, but only with rectangular mortises, and usually without much (any) tapering.  A couple things which I think contributed to this:

  • These tenons had flared rounded mortises.  Flaring the mortise with a file was a bit of a struggle..  perhaps if I had a 3/8" round file, it would have been easier.  With a 1/4" round file, it was a lot of work not to start creating grooves.
  • I used my dovetail saw to cut the slots in the tenon for the wedges.  Previously I have always done this with a bandsaw. I suspect the difference in kerf probably would have helped get a deeper seated wedge.


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Offline ChuckM

  • Posts: 1980
Re: krenov style sawhorses : mistakes were made
« Reply #1 on: August 04, 2020, 01:11 AM »
Yes, the Krenov sawhorses are wonderful. I have two pairs, one made by hand, and the other using domino joinery. I made all of them with fir for their light weight. I can carry all of them (one pair per shoulder) in one go.