Precision

[charlese]

First of all, I send along many thanks to Ed for reading his Magazine and starting this thread. This is one of the most thoughtful threads related to "good enough" - "accuracy" - "precision" and the unique qualities of wood. Thank you all for your input!:) Thought I'd wait until I read the article before posting. Didn't realize it would be some 50 posts later. I knew it would be a few days before receiving my copy of "Wood", as the delivery time to my house has previously lagged Ed's by a week or so. Just got my copy today and enjoyed the article.

There is one particular paragraph in the article that summarizes this good enough concept and I think it is worth repeating here, for those that don't read that mag. Here it is:

"Wood is pretty amazing stuff. It seems so substantial, yet it constantly moves in response to changes in temperature and humidity. Woodworkers for centuries have understood this and adapted their methods of work to account for it."

We all need to think about these three sentences before becoming frustrated that our machine is "off" by a couple of thousandths more than we think is proper. We need to think of this when we think that joinery MUST be absolutely dead on to be effective.

In reality there have been more joints fail because of conflicting wood grain movement than imprecise machining and from other natural wood properties like oxidation that resists glue adsorption.

[JPG]

Oops, a craftsman I shall never be
for to me
a fine tuned machine is a necessity.!

A 'Craftsman' may not need a finely tuned machine, but they sure make things a lot easier!

[Ed in Tampa]

First of all, I send along many thanks to Ed for reading his Magazine and starting this thread. This is one of the most thoughtful threads related to "good enough" - "accuracy" - "precision" and the unique qualities of wood. Thank you all for your input!:) Thought I'd wait until I read the article before posting. Didn't realize it would be some 50 posts later. I knew it would be a few days before receiving my copy of "Wood", as the delivery time to my house has previously lagged Ed's by a week or so. Just got my copy today and enjoyed the article.

There is one particular paragraph in the article that summarizes this good enough concept and I think it is worth repeating here, for those that don't read that mag. Here it is:

"Wood is pretty amazing stuff. It seems so substantial, yet it constantly moves in response to changes in temperature and humidity. Woodworkers for centuries have understood this and adapted their methods of work to account for it."

We all need to think about these three sentences before becoming frustrated that our machine is "off" by a couple of thousandths more than we think is proper. We need to think of this when we think that joinery MUST be absolutely dead on to be effective.

In reality there have been more joints fail because of conflicting wood grain movement than imprecise machining and from other natural wood properties like oxidation that resists glue adsorption.

Chuck
Great observation! In one of my earlier posts I mentioned my neighbor redoing furniture some of which is hundreds of years old. One of things I first noticed is most of the pieces that lasted that long is a joint I never see used today. That is a pinned mortise and tendon joint.

This joint is made by making a fairly tight mortise and tendon but after the joint is put together in final assembly on the back side of the joint a hole is drilled through the joint and a dowel inserted locking the tendon into mortise.

The glue may fail, the joint may have too much slop, but the joint does not fail. I really believe this one factor is biggest reason the pieces survived as long as they have. It wasn't the exceptional close tolerances, it wasn't the exceptional fine craftsmanship it was the fact the craftsman that built the piece knew how to insure his joint wouldn't fall apart.

[shipwright]

"Allowed Tolerance" X Number of Steps = Final Result
The point here is that many jobs require very close tolerances AND involve many steps. I do a fair bit of veneer work with multiple inlays and inaccuracies will stick out like a sore thumb. Given that perfection is illusive it is important to be as accurate as possible because each little"miss" will be magnified in each succeeding step of the process. By the end of a multistep process that 64th of an inch that seemed insignificant in the first step is now a glaring 1/8" (or worse) missalignment that draws the eye like a red flag.

Close enough is of course by definition close enough, it's
just that "close enough" varries widely from job to job.

[robinson46176]

Chuck
Great observation! In one of my earlier posts I mentioned my neighbor redoing furniture some of which is hundreds of years old. One of things I first noticed is most of the pieces that lasted that long is a joint I never see used today. That is a pinned mortise and tendon joint.

This joint is made by making a fairly tight mortise and tendon but after the joint is put together in final assembly on the back side of the joint a hole is drilled through the joint and a dowel inserted locking the tendon into mortise.

The glue may fail, the joint may have too much slop, but the joint does not fail. I really believe this one factor is biggest reason the pieces survived as long as they have. It wasn't the exceptional close tolerances, it wasn't the exceptional fine craftsmanship it was the fact the craftsman that built the piece knew how to insure his joint wouldn't fall apart.

When properly done you do not drill all three layers at once. You drill through the mortise part first then you insert the tenon tightly in place and mark the hole location. Then you pull the tenon out and drill just a little off center of the mark so that as you drive the pin in during the final assembly it draws the joint tightly together.

[Ed in Tampa]

When properly done you do not drill all three layers at once. You drill through the mortise part first then you insert the tenon tightly in place and mark the hole location. Then you pull the tenon out and drill just a little off center of the mark so that as you drive the pin in during the final assembly it draws the joint tightly together.

Interesting observation but the old craftsman accomplished the same thing another way. We were forced to destroy the joint to repair the piece of furniture. Once we got it apart we found out the craftsman used a tapered plug. It looks like the craftsman that build the piece first drilled a hole through the inside wall of the mortise, through the tendon and into the outside wall of the mortize. Then the hole on the inside wall of the mortise which was on the inside of the piece was cut to fit tight on the plug.
The hole in tendon was done so that taper of the plug pulled the joint tight.
and blind hole in the opposite of the mortise was cut to lock the taper plug into position. Therefore as the plug was pounded into the joint it's taper pulled the tendon tight. Interestingly the plug ended up firmly seated in each section. It accomplished what you said but it did it with a taper plug instead of offset holes. Great idea held for over 2 centuries but nearly impossible to take apart if repairs were needed.

[cv3]

I have enjoyed this thread. I have had some issues with alignment on my SS. I orderd the DVD on alignment last week. I align every thing as best I can. I use a combo square, angle gage and a level. This has done the job for the projects I have done so far. But all of the things I have done have been very basic. Things I am cutting out to carve, for the most part, do not require a great deal precision. Most of the time I use the band saw, sanding disk, lathe or drill press. I do not use the table saw on a regular bases. I have gotten interested in making boxes the last month and along with my fire place mantle project and I have noted that things are not as aligned as they need to be. I have spent a number of hours with my books tying to get it right. It is better but I am hoping the alignment video will give me some more guidance.

[BigSky]

I have enjoyed this thread. I have had some issues with alignment on my SS. I orderd the DVD on alignment last week. I align every thing as best I can. I use a combo square, angle gage and a level. This has done the job for the projects I have done so far. But all of the things I have done have been very basic. Things I am cutting out to carve, for the most part, do not require a great deal precision. Most of the time I use the band saw, sanding disk, lathe or drill press. I do not use the table saw on a regular bases. I have gotten interested in making boxes the last month and along with my fire place mantle project and I have noted that things are not as aligned as they need to be. I have spent a number of hours with my books tying to get it right. It is better but I am hoping the alignment video will give me some more guidance.

I won't have much to say on this subject. Some of those who do get pounced upon but if you need precision and repeatability from your SS it can be done. If you go this route just make sure that everything is locked both during alignment and during use. If you do an alignment with the carriage lock loose for example and then tighten it to do work you'll experience several thousandths of an inch movement. No fancy tools are needed. Just a good square and a straight edge <i use my level>.

[charlese]

I won't have much to say on this subject. Some of those who do get pounced upon but if you need precision and repeatability from your SS it can be done. If you go this route just make sure that everything is locked both during alignment and during use. If you do an alignment with the carriage lock loose for example and then tighten it to do work you'll experience several thousandths of an inch movement. No fancy tools are needed. Just a good square and a straight edge <i use my level>.

You're right on there, Mark! We need to remember to tighten the "5" locks.

[keakap]

However, if you want accuracy to within 1/1000ths of an inch, you got some work to do. Just know that it can be achieved using your Shopsmith Mark V.

This extension of the topic has been quite interesting. Made me think of two things:
1. A friend (now) who is a true artist in ceramics has his best day when he sells a very nice piece to someone who Really likes it, at a give-away price so the buyer can afford it.

2. I get all wrapped up (bound) in those thousandths on a cross cut of a fine piece of wood. When I get too wrapped up (frustrated-- a false frustration) I grab another piece of that wood and try to get a perfect cut with hand tools.

Talk about a study in relative "close enough"!