Half Blind Dovetail Drawers

[Mac Cambra]

What are the most common reasons for half blind dovetail drawers twisting and not sitting flat?

I am using a Leigh D4R. I am using HB dovetails for all 4 corners and making the dovetails on one side of the jig, as opposed to doing half on the other side.

Am I committing any obvious sins? The individual HB dovetail joints seem to fit pretty well.

[Sean Hughto]

Are the ends of the boards square to the long edges?

[Lee Schierer]

The most common reason is that the right and left side stops are not set the same or you didn't get all the pieces tight tothe side stops before you made your cuts.

[Karl Brogger]

The most common reason is that the right and left side stops are not set the same or you didn't get all the pieces tight tothe side stops before you made your cuts.

That and the ends of the sides not being cut square, or not being in the jig square.

[roman fedyk]

Aren't the sides of the D4R machined into the unit, so the sides cannot be out of square or otherwise mis-adjusted. Could be that there may some twist in the boards. The clamp can take some twist out but will probably spring back when unclamped. The board also must be very square, as other posters have pointed out.

[Scott Rollins]

I found that no matter how hard I clamped down the boards on my d4 the boards would slip and the boards would have angled dovetails (small amount maybe a degree or two). After adding some self stick sandpaper (actually stair tred tape) to the clamp bar faces the problem went away. You could try clamping some folded sandpaper betwee n the clamp bar and the wood to see if it helps. do not put sandpaper between the jig body and the wood it will throw off all of the registration marks on your jig by the width of the sandpaper.

[Karl Brogger]

I use the older Porter Cable jig. Sandpaper is a heck of a good idea.

[Jacob Mac]

Skateboard tape is great for these types of applications. It is super grippy, and it does not leave a residue when you remove it.

[Mac Cambra]

I will give your suggestions a try, I have one of the boards move on me but that was quite a bit and it got discarded.

I guess I could be getting the same movement to a lesser degree.

Thanks,

Mac

[John Keeton]

Just as an observation, a very small deviation from square makes a huge difference. For instance, with a 20" deep drawer, being out by .5 degree at the dovetail end would throw the other end out by .17 inch - nearly 3/16".

[Mac Cambra]

I just measured the squareness of my drawer stock and found that the end was a full degree out of square, 89 degrees. It is an 18" deep drawer and the drawer is twisted out and deflected up on one corner by 1/4 to 1/2 an inch.

I think we may have found the cause.

[Chip Lindley]

A very accurate try square or even a machinist's square in the shop makes thing FIT mucho betta!

Also, dial calipers to measure finished stock thickness in .001's of an inch. Moderate deviance in thickness can throw dovetails out of whack too!

[Mac Cambra]

I think I found the culprit, the pin/tails template bar was not set at a consistent height end to end. The net effect was that the depth of cut was not consistent on one of the tail boards. I measured across the tails on the affected board and the difference from onside to the other was about 1/16".

I think the fact that my boards were out of square as well was adding insult to injury. I say this because I fixed the issues with the drawer stock and the problem was improved but not eliminated. Then I noticed the tail height and realized the cause.

Thanks all for getting me thinking along a logical troubleshooting line.

Mac