Tolerances.. how tolerant are you?

[Steve Jones]

Some of you (those that didn't just go totally ot) have skirted close, but here's my 2c

The most dangerous tool in my shop is the tape measure - caused way more accidents than the power tools.

I seem to remember reading somewhere a quote from Sam Maloof, he doesn't use a tape measure much either.

If you're building chairs, leave the tape in the box, make it so it looks right and then check that it feels right.

If you're building a row of cabinets that have to fit between some walls (which are usually difficult to move) better use the tape.

A family member once brought a young relative of ours to my shop to start as an apprentice, they had supplied him with his very own brand new shiny tape measure, as soon as his proud parents left I took away his tape and told him he could have it back when he had learnt that he didn't need it. - we we're doing lots of built-ins at the time and when you want to cut a board to fit the alcove (or whatever space) I was taught (and passed on to him) that you're asking for trouble converting some distance to inches (or whatever) by measureing (and hopefully remembering) and then transfering that measurement (with another measuring) to the subject piece and then finding it is close - better to mark the board directly whenever possible.

 

[Corwin]

Corwin I agree go for the best you can get. Make that 4 ' cut to within .010 and bring it to my house. It may be WAY off. I think you can not find the answer because you did cut the wood accurately and the internal stress of the wood itself and/or environmental factors either immediately or over time changed the results. Especially results to the tolerances you are talking about.

Obviously with hardwoods and soft woods you assume they will change dimensions and therefore build  items with that in mind.
But when you are getting down to .01, even plywood or MDF can show movement. Yes, even plywood can change due to many environmental and/or manufacturing factors.

So when you can not find the problem, for piece of mind just blame it on that and go on. I have been caught in this trap only to find only I could see the discrepancies.

Nickao

Nickao,  Thank you for addressing my perspective directly.  Having past experience with precision machining, I had always hoped to bring at least some of that into my woodworking.  I do realize that wood, and even sheet material, can and do have movement.  As a beginner, much of the wood movement thing is understandable to me, but I do not yet have the experience to understand just how much that equates to, and all the circumstances when it comes into play.  But the information is out there, and over time I too will learn more -- hopefully, enough to get me past issues like this one.

So, as I said, I am interested in what the responses are to the original topic, as in this I may come away with a better perspective as to what tolerances are reasonable, and what levels are attainable.  Thus far, when I'm very close and cannot seem to get past that point, I have accepted that it was going rather well and yet I hoped to improve.  I'll still go for the gold, but I may sleep a lot easier with a better understanding of the limits one can actually reach.  

Thanks,
Corwin

 

[semenza]

Hi,

      Like many have already said,  the tolerance that I will allow is greatly dependent on the work. Even particular portions of the same work. I am always going for dead on.  In reality I don't allow any tolerance. In many ways the  tolerance is allowed by the work. Simply a function of how far out something can be and still fit.  And then beyond having the piece fit it becomes a function of what is allowable and still have the piece look good/ right.

Seth

 

[jonny round boy]

I heard this one from a guy who was a foreman in a furniture shop:

They had a new apprentice start, and, as was the case then, they assumed he knew nothing and taught him everything from the beginning. The first job was marking out & cutting timber.

They showed him how to do it, and then off he went to do it for himself. The result was that the piece he cut was too small.

So they showed him again, and off he went. Came back with a piece too small again.

So, the foreman asked the apprentice to show him how he'd done it. Foreman watched him, and he did everything correctly, but the piece was still too small!

After a lot of head scratching, the foreman inspected the apprentice's tape measure. Turns out he'd bought it second-hand. At some point in the past, the metal hook had snapped off the end, and someone had cut 1/2" off the tape, and rivetted the hook back on!!!

 

[nickao]

I heard this one from a guy who was a foreman in a furniture shop:

They had a new apprentice start, and, as was the case then, they assumed he knew nothing and taught him everything from the beginning. The first job was marking out & cutting timber.

They showed him how to do it, and then off he went to do it for himself. The result was that the piece he cut was too small.

So they showed him again, and off he went. Came back with a piece too small again.

So, the foreman asked the apprentice to show him how he'd done it. Foreman watched him, and he did everything correctly, but the piece was still too small!

After a lot of head scratching, the foreman inspected the apprentice's tape measure. Turns out he'd bought it second-hand. At some point in the past, the metal hook had snapped off the end, and someone had cut 1/2" off the tape, and rivetted the hook back on!!!

And that is why I measure the least amount possible, or use the foreman's tape. We used to synchronize our tapes with our "cut man" for jobs that were simpler to just have one guy cutting on the ground and two or three working up top. It's unreal how much even two brand new tapes can differ.

Nickao

 

[Michael Kellough]

I heard this one from a guy who was a foreman in a furniture shop:

They had a new apprentice start, and, as was the case then, they assumed he knew nothing and taught him everything from the beginning. The first job was marking out & cutting timber.

They showed him how to do it, and then off he went to do it for himself. The result was that the piece he cut was too small.

So they showed him again, and off he went. Came back with a piece too small again.

So, the foreman asked the apprentice to show him how he'd done it. Foreman watched him, and he did everything correctly, but the piece was still too small!

After a lot of head scratching, the foreman inspected the apprentice's tape measure. Turns out he'd bought it second-hand. At some point in the past, the metal hook had snapped off the end, and someone had cut 1/2" off the tape, and rivetted the hook back on!!!

And that is why I measure the least amount possible, or use the foreman's tape. We used to synchronize our tapes with the cut man for jobs that were simpler to just have one guy cutting on the ground and two or three up top working. It unreal how much even two brand new tapes can differ.

Nickao

It's true that different tapes are incremented slightly differently and that can be very annoying.

The story above seems apocryphal to me though (or a bit odff in the details) because if the kid did the measuring and cutting himself with his own tape the piece would fit. If the piece was short it's because the initial measurement was made with an different (unmodified) tape.

 

[dirtydeeds]

same story but different

i was teaching a pair of young carpenters how to repair box sash windows

so one of them measured up the staff and parting beads while the other one cut

they both used their own tapes  :

 

[slb]

I once took a course from an instructor whose motto was "better is the sworn enemy of good enough", his point being, of course, that one often makes something worse by trying to eliminate the last little imperfection 

For me, precision is almost always more important than accuracy.  That is, I want parts to match each other as perfectly as possible but I usually don't care if they are 1/32 inch or 1 mm off of the intended size from the plans.  Wood will shrink and swell as the seasons pass anyway - typically by about 1% in width (1/8 inch per foot!), so an exact measurement is a temporary thing at best.  But an uneven reveal around a door, a gap where a joint wouldn't pull closed, or a step where two pieces don't meet evenly is ugly forever.

So, I do three things:  1) I try to plan my cuts so that once I get a machine or jig set up I do all of the parts at once that share that planned size.  That way they all match even if they are "wrong".  2) When I can't do all the cuts at once, I use one of the previously cut parts as a setup gauge when I need that size again, instead of measuring anything.  3) Whenever two independently made parts need to fit together, I leave some extra on one of them and trim it to fit the other once they are all done.

And then I cuss a lot when despite all that they don't match  ;D

 

[Michael Kellough]

I once took a course from an instructor whose motto was "better is the sworn enemy of good enough", his point being, of course, that one often makes something worse by trying to eliminate the last little imperfection 

For me, precision is almost always more important than accuracy.  That is, I want parts to match each other as perfectly as possible but I usually don't care if they are 1/32 inch or 1 mm off of the intended size from the plans.  Wood will shrink and swell as the seasons pass anyway - typically by about 1% in width (1/8 inch per foot!), so an exact measurement is a temporary thing at best.  But an uneven reveal around a door, a gap where a joint wouldn't pull closed, or a step where two pieces don't meet evenly is ugly forever.

So, I do three things:  1) I try to plan my cuts so that once I get a machine or jig set up I do all of the parts at once that share that planned size.  That way they all match even if they are "wrong".  2) When I can't do all the cuts at once, I use one of the previously cut parts as a setup gauge when I need that size again, instead of measuring anything.  3) Whenever two independently made parts need to fit together, I leave some extra on one of them and trim it to fit the other once they are all done.

And then I cuss a lot when despite all that they don't match  ;D

Good point. You could boil it down to fit is more important than fidelity.

 

[Fred West]

I once took a course from an instructor whose motto was "better is the sworn enemy of good enough", his point being, of course, that one often makes something worse by trying to eliminate the last little imperfection 

For me, precision is almost always more important than accuracy.  That is, I want parts to match each other as perfectly as possible but I usually don't care if they are 1/32 inch or 1 mm off of the intended size from the plans.  Wood will shrink and swell as the seasons pass anyway - typically by about 1% in width (1/8 inch per foot!), so an exact measurement is a temporary thing at best.  But an uneven reveal around a door, a gap where a joint wouldn't pull closed, or a step where two pieces don't meet evenly is ugly forever.

So, I do three things:  1) I try to plan my cuts so that once I get a machine or jig set up I do all of the parts at once that share that planned size.  That way they all match even if they are "wrong".  2) When I can't do all the cuts at once, I use one of the previously cut parts as a setup gauge when I need that size again, instead of measuring anything.  3) Whenever two independently made parts need to fit together, I leave some extra on one of them and trim it to fit the other once they are all done.

And then I cuss a lot when despite all that they don't match  ;D

Good point. You could boil it down to fit is more important than fidelity.

Michael, you could that. So how many times married??? : 8) Fred

 

[Ned]

Good point. You could boil it down to fit is more important than fidelity.

Michael, you could that. So how many times married??? : 8) Fred

An example of one of the reasons why I like FOG is Michael's turn of phrase.

Another is the way Fred turned it.

 

[ccmviking]

      I generally measure and mark everything to 1/32", which is about the best I can do with a .9mm mechanical pencil (I just keep breaking everything under a .9mm because I write too dang hard).  Day in and day out I'd say 1/32" is what I work in.  Would my feeling be hurt if a cabinet carcass piece is within a 1/16" ? No, of course not.  You need to try to keep your "tolerance" in the same direction if possible.  You don't want it over a 1/16" on one end and under a 1/16" on the other.  I would call that an 1/8" off.  Sitting here, what I think of as not being tolerant of any error that I do is splicing molding, especially crown.  If you're off on that, it will definitely show.  Another thing when I mark and cut I always split the pencil mark, meaning in the middle of the mark is my measurement.  The mark could be wide or narrow and my eyes have to half it.  May not be the best way but it's fast and works well.  How do others mark to cut when you're doing lots of marking and cutting.  (and don't tell me you all carry razor blade around in your pocket).  Left, Right, Center??? 

Chris...

 

[Michael Kellough]

Good point. You could boil it down to fit is more important than fidelity.

Michael, you could that. So how many times married??? : 8) Fred

Very funny Fred, I totally missed that take.  I have a tendency to miss that kind of innuendo. Back in college I took a class called the "religious dimensions of the arts". The religion Prof teaching the class had a very conservative taste in art and I tended to read while he talked. Near the end of a discussion of J.S. Bach the thread had wandered to the secular aspects of Bach's life and the teacher mentioned that Bach had 7(?) illegitimate children and I chimed in with "and he also had six organs". Everyone but me exploded in laughter and the class had to be dismissed. I was just thinking of the category of large quantities of superfluous accessories. 

I have much different standards for marriage, fidelity trumps. I've been living with the same sweetie since she helped me recover from a bad case of mono in 1975. We finally got married a couple of decades ago.

 

[Eli]

How do others mark to cut when you're doing lots of marking and cutting.  (and don't tell me you all carry razor blade around in your pocket).  Left, Right, Center??? 

Chris...

I put the laser right on the line. That's generally within a mm. I try to always cut to the marked side of the line, ie, put one side of the line itself at the mark, doesn't matter to me which side.

 

[Fred West]

Ned, thank you for noticing the turn of phrase. 

Michael, I just about laughed myself silly when I read your Bach adventure.  I love accidental misspeaks like that and my g/f, fiance is of the same ilk as in saying the same kind things. Luckily she like it seems you also enjoy it even if it is after the fact.  Congrats on you and your sweetie as I think that is wonderful. Fred

 

[Michael Kellough]

Ned, thank you for noticing the turn of phrase. 

Michael, I just about laughed myself silly when I read your Bach adventure.  I love accidental misspeaks like that and my g/f, fiance is of the same ilk as in saying the same kind things. Luckily she like it seems you also enjoy it even if it is after the fact.  Congrats on you and your sweetie as I think that is wonderful. Fred

Thanks Fred. On the other hand I can't figure out why everyone says they dislike puns. Seems to me a pun is just a dry joke. What's wrong with that?

 

[Fred West]

Michael, got me I love puns and every other form of humor.  ;D Fred