POLL - Is a 1/8 tolerance considered precision fabrication?

Is a 1/8 tolerance considered precision fabrication?

  • Yes
  • No
0 voters

I deal with stuff that’s that far out or more, from time to time. It causes a lot of problems.

If 1/8" is considered “precision,” then I guess I can rest on my laurels as a hobbyist. I would happily pay somebody who could get within 1/64" on stuff at higher volume than I can do quickly, but I can hit pretty tight tolerances in terms of measurements on a lot of stuff just being careful/slow and methodical.

Just yesterday I got almost all of a large group of holes cut with an annular cutter within .002" placement with nothing but hand tools, a mag drill and a lot of care and fussing. If I can do that without much experience in fabrication, I would expect a lot from a pro fab shop.

Welding throws in shrinkage and distortion. If stainless steel, multiply the problem by a lot. You’re comparing apples to oranges.


It depends. How big is the workpiece?


Precision is measured in thousandths and often includes machining. If I’m making general fabrication stuff like gates, rails, stairs, etc a sixteenth is acceptable. It depends on a lot of factors like are you talking about hole centers in relation to the fabrication?


Depends, 1/8" compounding linear error, 1/8" per foot, or 1/8" per 10 foot.


I work in data science for a living, but as a hobbyist I have built furniture, houses, kitchen cabinets, etc. From data science to my hobbies, there is no single metric that you can use to answer a question, every question needs context plus metrics to be answered. Each task in life has an acceptable tolerance, often decided by the context. If I were comparing diagonal measurements to check for square, 1/8" across 50 feet might be fine but 1/8" across 1" is terrible. At 50’ that might be the the difference in the sag of the tape measure…


It is totally fine if you are clearing out a shoreline of a lake with a nuclear explosion…

Red Flag ! I would want more info on the job, because specifying a ± 0.125" tolerance, means that Q.C will pass parts that are longer, shorter, thicker, thinner, etc by 0.125". This wouldn’t work for assemblies with multiple parts that are expected to fit together quickly on an assembly line to make money. In contrast, this tolerance would work for a single part such as a paperweight.


Most fabricators just throw this tolerance around. I agree it needs more context but most of the time it becomes a default for all fabricators.

Jason- Please recommend where I should post replies to posts outside GD&T that relate to GD&T. I’d like to keep the topic from spreading all over the forum (it becomes hard to track and respond to questions).

This tidbit from the ASME standard Y14.5M 1994, 1999, 2004 revisions: (similar language exists in all later revisions)

Dimensioning and tolerancing shall clearly define engineering intent and shall conform to the following.
(a) Each dimension shall have a tolerance, except
for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size). The tolerance may be applied directly to the dimension or indirectly in the case of basic
dimensions, indicated by a general note, or located
in a supplementary block of the drawing format…

From this rule comes the notion that dimensions must be toleranced. But simply adding ± to design dimensions is often a less-than-satisfactory solution.

Make a new post in the general section.

Really need to add a selection… " It depends"
What you are working on will dictate the level of precision and repeatability you need. I work on stuff that has tolerances as small as +/-.0002", all the way up to +/-1/2". We create holes at work that have tolerances that at +/-.005" are not considered close tolerance, but others at +/-.001 that are.

Tolerances need to be defined by the accuracy actually required and the cost to make them at that accuracy for both location and size, and whether any other defining information is relevant and reflects what is achievable in the particular material. A .005" tolerance in wood is nearly impossible in anything but extremely controlled circumstances, but then the same dimension in steel or aluminum is not a big deal.

1 Like

Hey Jason,
I think it’s a natral evolution in any trade for people to set new bars and bring in the tolerance who knows where we will be in 50-100 years look how far we have come over the last century. I am just finishing welding tech so I am new to this trade but have decades in “The Trades” Broke my back and thats all she wrote for my former career in carpentry and concrete… said that to get to this. I plan to build my new business around holding myself to as high of standards as I can achieve and although I am going to struggle to get the equipment necessary because the financial pickle my disability has put me in i think as craftsman if you are not pushing yourself then why not do something els. We don’t do it cause the money is easy thats for sure. I’m not on some soap box and right now I know that most the people on this forum would smoke me as far as quality. (but I’ll get there.) I’m going to shoot for the dragon wagon and work my way up. I am wondering when you say 1/8" tolerance over what type of distances are we talking? I would like to set some goals. oh and before people jump all over this about me coming from the general contracing world. I do know pretty tight tolerances I also spent quite a spell in plastic injection processing and tool making for aerospace. there is a place for both loose and tight tolerance, but I would like to be capable of holding as tight as some people claim. sorry about the rant. just wondered if its like 1/8" over 5’ ?10’? 20’? I would like to say thanks to all the tool builders that make awesome tools that help put food on my families table. I look forward to working with you.

This is a great point also many parts are left with a loose tolerance to cope with working environment as well as assembly. the kolesnikov is commonly referenced for this reason.

!/8th COULD be considered precise perhaps if it were over the length of 50ft.

Additionally, a print can have a NOTE where the tolerance requirement applies to all dimensions (Ex: ALL TOLERANCES 0.0625" UNLESS OTHERWISE NOTED). With that said, that same print can have specific tolerances callouts as required.

I feel like that depends on the size. 1/8” on a box that’s 18 inches long? No. 1/8 inch on a 15 foot long piece? Absolutely.