robdurante

What is an acceptable woodworking tolerance?

Recommended Posts

I'm a serious hobbyist, but my profession is a Scientist.  I design an build my own furniture.  I often wonder what is a good tolerance to take my final part size to.  

 

I typically machine mill flat and square, then rough size the parts.  After stickering, and adjusting the part flat and square again, and perhaps doing the centered M&T, I will hand plane down to the finished size.  One can get each board exact if needed, but is is really needed?  I typically plane to +/- 0.010 inches (mostly + 0.010).  I wonder what others do.  I find this a pretty good tolerance to do final smoothing after assembly to match up the pieces well.

 

Can other share their thoughts on tolerance?

Share this post


Link to post
Share on other sites

Im pretty exact and work from plans but don't know that I've measured down that far. I rely on order of operation to get things exact. For example I wouldn't sand door parts flush, they are flush when assembled just due to the order of the milling process.

Share this post


Link to post
Share on other sites

I'm a scientist, too, and I use my woodworking hobby to get away from that sort of measuring.  If my fingers and eyes can't tell the difference between two pieces, then it is good enough.  If they can, a few swipes of a plane or scraper changes that.  Like Mike said, if it is a one off piece then all that matters is that pieces that need to be the same are the same, whether they're 12.5" or 12.75" long doesn't matter much.

  • Like 1

Share this post


Link to post
Share on other sites

I don't know that I would be happy with relative dimensioning thing and being off by much, to OCD for that. I do think some take all the marking and dimensioning a little to far. I watched a WW TV show this last Saturday and the guy marked out all his mortises nice and pretty then went to the HCM to cut them all out using the fence. Makes no sense to me what so ever. Adjust the machine and they are going to be what ever you set the machine to all those markings and using a pretty little marking gauge isn't going to change a thing. I think sometimes you just need to use some common sense.

Share this post


Link to post
Share on other sites

I'm not a scientist, but I do have to deal with nitty gritty small details in my work.  I agree with Gilgaron in that if my fingers can't tell the difference, it's the right size.  I do this for fun, so I don't want to worry about if I'm within 10 thou.  Just my opinion though, so take it for what it's worth.

Share this post


Link to post
Share on other sites

I only worry about tolerance in joints and show / reference faces. The back doesn't usually matter, and woods moves over time anyway.

 

That pretty much sums up my view....joint tolerances, proportions, and appearance are more important to me than getting the intended dimensions to the gnat's eyelash.  Obviously you've got to use some good judgement where structural integrity is involved, but does it really matter if a table top is 5/4" thick vs 9/8", or leg 3-1/16" thick vs 3" thick?  

Share this post


Link to post
Share on other sites

It depends on what you are building. If it is a one-off piece, if it looks good and fits good, it is good. If you are batching out interchangeable parts then tolerance matters. But like PB said, even then if you use identical machine settings you should get identical results.

 

Mostly this.  If I'm making a piece that is a built in that needs to fit in a specific space, then I try to stay pretty close.  But for the most part, I worry about it looking good.

 

It doesn't matter if my end table top is 1.5" thick or 1 5/8".  The length of my aprons dont matter as long as the opposite ones are the same length.

 

Obviously you want your joinery to fit nice and tight, but beyond that I dont much see the point in worrying over a few thousandths here or there.

Share this post


Link to post
Share on other sites

Sometimes 1/16" is no biggie. Sometimes it's huge.; a gap in a joint vs a panel size for example. I set up shaper heads to .001" but my parts may vary by .03" from time to time. It all ends well though. In the end this is wood not metal. Plane it, sand it, fair it out and move on.

Steve

  • Like 1

Share this post


Link to post
Share on other sites

The thing is like with any building process you don't need to hold the same tolerances over a whole piece.  There are times when you need at least precision if not accuracy in your work or you will have crappy joints that either don't fit or have very noticeable gaps.  But flatness of a table top, over the whole surface 1/32" could be pretty hard to notice I think, and maybe 1/16".  More than that I think would be likely to be noticed without a detailed inspection.

 

Also as it is precision that matters most if the pieces are off in the same way it will be unnoticed. 

Share this post


Link to post
Share on other sites

I don't put OCD into numbers...I seek perfection and accept acceptable.  If it doesn't fit right or look right, it ain't right.  If it does, it is.  We all have different opinions on what acceptable is.  It also depends on what kind of work you do...guys who do rustic pieces have a great excuse to do sloppy work.  People who build contemporary or studio pieces have to be more careful.

Share this post


Link to post
Share on other sites

Just want to throw out there, since all of your machines, plans, and podcasts will talk in fractions (sorry metric people)... I never go more precise than 1/64, because that's what my favorite ruler is in. Most of the time is stop at 1/32 unless we're talking visible joinery.

 

If you do your own designs, I guess you don't need to worry about that part...

Share this post


Link to post
Share on other sites

When milling solid wood I will only cut the pieces I can make the joinery on in the same session or next day. The tolerances I use are plus or minus a midgies didge. So if the board is intended to be 3/4" nominal thick I will get it to as close I can + or minus a few thou according to what my calipers say. Then I will try to do all the joinery for those pieces.

When glued up and planed/sanded I don't care whether it is 3/4" or  47/64" or 23/32" thick. It doesn't matter. As long as the joints are tight I'm good to go.

 

I fit drawers to case work but I try to get internal dimensions of the openings as close as to the design as possible, That way the "same size" drawers are interchangeable,

 

When making guitars I will make sure that the salient dimensions are all as per the design within a few thou on width and to 1/32" on length - this is achievable on such relatively small items. This would be the width of the neck at the headstock end, the wider width at the body to neck joint, the relative position of the bridge to the nut. I always use routing templates for the headstock and neck joints so know they will always be the same. For electric guitar bodies I make a sawing/routing template first of all for repeatability, Again the profile template can be any shape and wouldn't necessarily have a tolerance on it. Just as long as it can be reused I can make another body of the same shape identical to all the others.

When cutting fret positions I would always work from one end to avoid cumulative errors that occur when measuring between frets. I would work to a tolerance of a few thousands over 18" or so but rely on mitre boxes and calibrated fret rulers/template to achieve that.

When mass producing guitar manufacturers invest heavily in CNC equipment that works to 1 tenth of a thou in a few feet. Hobby woodworkers don't have and don't really need that luxury.

 

So tolerances matter on certain applications. No customer I have come across uses a micrometer to measure the thickness of a tabletop and pull you up about it. They just don't care. If it looks right it is right.

Share this post


Link to post
Share on other sites

When milling solid wood I will only cut the pieces I can make the joinery on in the same session or next day. The tolerances I use are plus or minus a midgies didge. . .

 

 

 That's another reason I could never learn the metric system. There's probably dozens of those "midgies didge" phrases I'd have to learn :unsure:

  • Like 2

Share this post


Link to post
Share on other sites

 That's another reason I could never learn the metric system. There's probably dozens of those "midgies didge" phrases I'd have to learn :unsure:

:D Ken a midgy is the name for a mosquito like insect. The didge is slang for what the male one uses to procreate   :P

So the dimension isn't very big! No need to learn new fangled metric.

Share this post


Link to post
Share on other sites

I'll be danged. Thanks Terry. Now I can be sarcastic to some of my male friends without them being the wiser !

Years ago, there was a song by an Australian where he said something like "watch me didgery do mate".  Same reference?

Share this post


Link to post
Share on other sites

No a didgeridoo is a musical instrument devised by the first nation Australians. It looks like a long pipe a few feet long and about 2" to 3" diameter that you blow into. It makes a really strange but pleasant noise and good players use circular breathing where you breath in through the nose and blow out with the mouth at the same time.

 

That guy was probably ex entertainer Rolf Harris. He's in jail now. Google him to find out why.

Share this post


Link to post
Share on other sites

DOES THAT PIPE HAVE TOLERANCES????? RE-RAIL..... :)

Y'all know the deal...a machinist's personality type is that he/she loves precision.  i have an Incra set up on my table saw and my router table.  I also have a metal lathe.  I love the precision of things .  I have to remember though that wood is definitely not the same as metal.  Tolerances depend on where the gap is and what's going on around it.  Tolerances depend on things like anticipated expansion WITH long grain or ACROSS grain. Maybe .050 with long grain and .150 expansion across the grain of the panel.  I'm sure glue makers have some numbers on tolerances for their glue to work properly ( i.e. mortise and tenon) Overall though, woodworking is cooperative dance between aesthetics, feel, function, and stability.

Share this post


Link to post
Share on other sites

Didgeridoo is a wind instrument. i beilive the song says "play" me or my didgeridoo.

So, i guess it would Not be the same reference.

Share this post


Link to post
Share on other sites

For some things, fingers and eyeballs will get you close enough.   If I'm going to run a hundred pieces of something, I'm going to set up as accurate as possible to save time in assembling all the pieces, even though they are all going to be hand fitted.  I have an old heavy, cast iron tenoning attachment that will run all the pieces I push with it pretty daggone close to being all the same.  These tenons were run to fit into 3/8" wide mortises cut in old Heart Pine.  You can't cut that stuff completely clean every time, so each mortise needed to be hit a few strokes with an Iwasaki x-fine wood file-hence the extra couple of thou.  There were 172 of these to be run and fitted.

post-14184-0-57032200-1423866965_thumb.j

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.