Machinists Expect Tighter Tolerenences

[Janderso]

I learned something about myself today.
I am at work building an 8’ x 30” transmission tear down/build table. You know, the fluid drains to the back and empties into a receptacle.
I am cutting the pieces of 2”X 3” tubing to length.
I wouldn’t be surprised if I was within .010” in length difference between all six legs.
That never would have happened if it wasn’t for this web site and the machinists I have met.
This is just a small representation of the frame of reference change we go through when we improve our skill set.
Every day is a new adventure in the shop.

 

[682bear]

I've heard my dad say many times that good machinists don't make good carpenters... I resemble that remark.

My dad, on the other hand, actually is a good machinist AND a good carpenter...

-Bear

 

[Janderso]

That reminds of my Dad's carpenter days.
He was in sales and pretty much mechanically retarded (sorry Dad).
He would try to fix the lawn mower, get mad, throw a screwdriver and leave. I would come along later and dink with it long enough to figure it out, in my early teen years anyway.
He did build a fence here and there due to our many moves.
Be it split cedar-grape stakes, or to a more contemporary project, every board and post was as perfect to true and level as his trusty ole Stanley could produce. His toe in nails were perfectly spaced and at the same consistent angle.
It was a marvel to watch. he was slow as cold molasses.
I miss him.

 

[derf]

I helped a guy build a transmission table years ago. The top was 3/16" thick, and for a drain, we fired up the torch and cut a 2" hole in the center. The heat of the torch warped the top just enough to give it a dip right at the drain hole.

 

[C-Bag]

I deal with customers all the time who don't seem to know how to read a tape measure. Inches seem to be inconsequential and the difference between 1/2" and 1/4" seems nit picky. Much less 1/16". So when I try to relay I constantly work in .001 and smaller I get no response. Sometimes I think metrology is just a way of describing a compulsive disorder

 

[RJSakowski]

I usually work to .001" for machining, .05" for sheet metal and 1/32" for carpentry. For cabinetry and joinery, I will measure and layout to 1/32"- and 1/32"+ along with 1/32". There are of course times when that accuracy isn't required. The trick is to know when you can loosen the tolerance.

When we did a full kitchen rebuild, we hired a contractor to help with the framing and rough carpentry. We were calling out dimensions to his helper who was cutting with a miter saw. The helper would be cutting to nearest 1/4" and I was checking the dimensions when he finished. When I mentioned that the cuts weren't accurate, the contractor yelled down the his helper "we're working to 1/8" today. Considering that the pieces in question were studs custom fit to a 100 year old structure, even an accuracy of +/- 1/8th was too loose in my book.

 

[Tom1948]

Worked with a guy once when we was nailing up some 2x 4 's . He started to drive a nail. I said hold it, your a 1/4 inch off. His reply "A 1/4 inch only matters if on the end of your d****. "

 

[GL]

Fully agree, machinists try very hard to hit the dimension. Practice when it doesn't matter so you can do it when it does. As RJ said, you have to know when you can loosen things up. As I was building my shop, I had to keep reminding myself that this was going to be a shop, not a 40x60 fine woodworking cabinet project. Things were not going to be seen ever again and a little gap (like 1/16, not 1/4) here and there was really going to be fine. OCD is when you start sanding the OSB for the walls?

 

[Bob Korves]

Machinist apprentice to journeyman mentor: "Those thousandths sure are small. There must be about a million of them in an inch."

I know a guy who manufactured utility trailers. He hired a young man, showed him how to use the chop saw, and told him to make a bunch of pieces of bar stock 21 13/16" long. The new hire got busy cutting a whole bunch of pieces, then went to the owner, pointed to the tape measure, and asked "Is this mark here 13/16?"

 

[Janderso]

Yes, the old Craftsman style, homes were truly made by Craftsmen. I like the built in cabinetry and crown moldings, square corners etc.
I had the opportunity to watch a neighbor finish his new home when I lived in Lake Tahoe.
His father was doing the finish work. He used an old manual miter box to cut the angles.
Needless to say, it took him a couple weeks and it was perfect!