[OP]
Member
What is the acceptable gap between pins and tails in half blind dovetails (I’m doing hard maple)?
I am able to get my gaps so close that I can barely slip .0015” feeler stock in – is this too tight? I love the way it looks though - but would it cause the stock to split in time after gluing?
Member
If you are cutting these by hand, leave the room and shut up!!!!!!!!!!!!
Heather
Any thing with sharp teeth eats meat.
Most powertools have sharp teeth.
People are made of meat.
[OP]
Member
Oh no - I was getting that on a router table using the Route-R-Joint jig from Woodline and a woodpeckers lift.Originally Posted by Heather Thompson
The joint halves should slip together with minimal effort or force. Remember the wood will swell slightly when the glue is applied. If the joint falls apart when dry fitted the joint is too loose. The parts should stay together without glue. If your parts have .0015 clearance per side or less you are probably perfect.
Lee Schierer
USNA '71
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Member
If it goes together without forcing it, you're good. That's it. No worries about the glue.
Jason Beam
Sacramento, CA
beamerweb.com
Moderator
Personally, I like to see the gap be no greater than 381,000 Å but that is me....
Sometimes I try to get it under 2 x 10^(-5) fathoms....
[OP]
Member
Cool! Do you also use laser diffraction spectrography to determine the gap width?
Member
.0000" would be the perfect fit, and what I shoot for.
OTOH, I do them by hand.
I thought machines were more accurate though...do you mean to tell me you can't get a perfect fit?
--
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Alan - http://www.traditionaltoolworks.com:8080/roller/aland/
Guest
I like mine just tight enough that you have to tap them together with a mallet. Not wailing on it, but just tapping.
Member
I shoot for fifteen queblors.
Seriously, do you want to know why you are getting so many smartass answers? It's because this is really a silly question (no offense intended). The thing is, this is not metal work. It's wood. I answered a similar question once when a carpenter asked me "what the tolerances were" for the fit of the joints on mitered door casings. "Zero". It either fits or it doesn't. Your dovetails are the same. They either fit or not. There are no "tolerances" or "acceptable gap". We are not talking about spark plugs. If you can tap your joints together with light hammer blows, you got em just right. If you have to beat on them, they are too tight. If they have gaps between the mating surfaces they are too loose.
David DeCristoforo
Member
Another way to measure, if you've seen good work before and are happy with your own dovetails, you've got them right. If they look sloppy you'll know it (or your friends will tell you).
Member
I've got to agree with Dave on this one...
Much too often we loose perspective on what we're really trying to accomplish. We are working with wood, not tool steel or precision machinery. The sawdust itself is larger than .0015 and the relative humidity will cause the wood to expand and contract more than this.
If a dovetail joint just slips together without resistance then it's too loose. These joints when assembled should require what I call a tap fit. The glue applied with be absorbed into the wood and when dry will be nearly impossible to separate.
Leave the precision to the machine shop and enjoy woodworking....
Member
I don't believe this is a silly question, it's a good one.
I posed a similar question when I attended a woodworking school some years ago. The answer I got from a very well recognized "expert" was about .003" Anything over that and the dovetails are too loose. Anything less than the perfect .000" and they are too tight.
The problem with this answer, and any others, is that we normally look at only one dovetail at a time, so if all of them fit perfectly except for one, then none of them fit; which is why we cut all the tails, or pins, first, then mark the the corresponding pins. It follows that the tails, again cut first, can be virtually any size and as long as the pins fit in relation the the tails then everything is fine.
There is of course, error in every single one cut. If the error is small, say .003" and you do a good job of cutting the pins you have a reasonable chance of everything going together. If you look very closely though, even in good fitting dovetails you will usually see some gaps and some that are very tight.
I try to cut mine, by hand, as tight as I can get them. When I test fit and I can see that it will assemble then I pound them home!!!!. If there is a little glue in the joint the small gaps disappear. If you have cleaned out the the "little crumblies that are between the tails and pins you will have a nice tight dovetail. I have seen many dovetails that were well cut with the saw but were not cleaned out and it will hold them apart from seating properly or can cause them to crack.
Practically speaking I would not quibble with any ones method, every one that has expressed and opinion is probably correct, but to get all those piece of wood to fit together requires a little gap or space, in my opinion it about .003"
Member
Well, most glue makers are looking for around a .003 to .005" glue film, so if you are getting .0015", there is not really enough room for glue. I like the .003" answer for most glue joints.
If these are for drawers, and made by machine, make a test box from scrap trying to achieve your .0015" gap, let the wood sit several days after cutting the dovetails, then rub glue all over those suckers and see if you can bang them together. Maple gets real chippy when you start banging it hard, I learned this the hard way. Seriously, bang out a quick sample and do a live glue test, and look at your results. This is a visual art more than a science. This will give you more information than I can or a set of feeler gauges can, unless you are making the dovetails as a birthday present FOR your feeler gauges, then by all means let them be your judge.
PS: I use feeler gauges to set up machines but it honestly never even occurred to me to use them for any other tests. At least one of us may need therapy.
[OP]
Member
Probably I need the therapy!Well, most glue makers are looking for around a .003 to .005" glue film, so if you are getting .0015", there is not really enough room for glue. I like the .003" answer for most glue joints...PS: I use feeler gauges to set up machines but it honestly never even occurred to me to use them for any other tests. At least one of us may need therapy.
On the .003 - .005 glue film gap, would that also apply to hot hide glue?
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