tolerances and accuracy

[DanielOB]

In fine-furniture we have Mictrometers, Verniers and Measuring-Tape. They have their own accuracy (or errs). We use "good" tool and they also have its own accuracy. We are not perfect and so have our own accuracy. Marking is with own accuracy, ...

1. In fine-furniture work what are acceptable toleranaces for lengths, you work with, and why?  [e.g. for short lengths: +/-1.2 mm, (+/-1/16), ...]
2. What you use as measuring tools and why, and be specific?  [e.g. manual mitutoyo vernier, PowerLock Stanley, ...]

Thank you

 

[semenza]

A 1/64th works for me most of the time but there are occasions such as visible joints (dovetails) where better is needed. But that is coupled with making all like cuts and pieces exactly the same by using stops etc.

Seth

 

[DanielOB]

Thanks Seth, and what you use to verify 1/64"
What marking tools you use to achieve 1/64"

 

[Carl Prentiss]

Daniel,
I think good planning and the use of stops or gang cutting will negate the need to actually measure and cut a piece to within 1/64, yet allow the end result to be within that tolerance. When it's necessary, direct marking and "sneaking up" will/can get you there. In the end, I care about tight, functional, good looking joints more than if a table is 1/64" taller or shorter than it's supposed to be.
-Charlie

 

[Rick Christopherson]

Most cuts don't need to be super accurate; just consistent from one to another. When precision between associated cuts is critical, your finger is the most accurate measuring tool you have. You can feel an error as low as 0.001" between two parts.

Take some framed tops I just made for a couple of side tables for example. The size of the main field plywood wasn't critical at all, aside from ensuring they were square. However, the lengths of the mitered frame are ultra-critical, lest you have visible joints. So for these, I park in front of the miter saw with all the parts and cut them to fit by continually trimming until they are perfect. The first miter is cut long, and tweaked (as needed) to ensure the angle is perfect to the previous piece. Then the length is trimmed to fit the next corner. Because I am right-handed, the left miter is the first one, and the right miter is the one trimmed repeatedly to tweak the length.

Oh, and instead of using a pencil, I use a utility knife to mark the length, as it leaves a more precise line than the thickness of the pencil lead.

 

[Rick Christopherson]

By the way, here is a tip for fine trimming a board. With the miter saw off, lightly press the board sideways into the blade's teeth or plate. Then raise the blade away and make the trimming cut. If you touch the blade plate, the trimming cut will be the amount of teeth protrusion from the plate (1/2 the difference between the plate thickness and the kerf of the teeth). And the harder you press the piece into the side of the blade (before the cut of course), the more deflection of the blade and the deeper the trim will be. You can use this to nibble away as little as 0.001" or as much as 1/32" at a time if necessary.

 

[grbmds]

Most cuts don't need to be super accurate; just consistent from one to another. When precision between associated cuts is critical, your finger is the most accurate measuring tool you have. You can feel an error as low as 0.001" between two parts.

Take some framed tops I just made for a couple of side tables for example. The size of the main field plywood wasn't critical at all, aside from ensuring they were square. However, the lengths of the mitered frame are ultra-critical, lest you have visible joints. So for these, I park in front of the miter saw with all the parts and cut them to fit by continually trimming until they are perfect. The first miter is cut long, and tweaked (as needed) to ensure the angle is perfect to the previous piece. Then the length is trimmed to fit the next corner. Because I am right-handed, the left miter is the first one, and the right miter is the one trimmed repeatedly to tweak the length.

Oh, and instead of using a pencil, I use a utility knife to mark the length, as it leaves a more precise line than the thickness of the pencil lead.

I might even take this a step farther. I am not measuring so much anymore. Where possible, I try to fit the length into the required opening but using the story stick idea. You can make your own, but I actually bought Woodpecker's Story Stick Pro and it really gives me better accuracy but taking the exact length within a particular space and then allowing me to transfer that to the piece I'm cutting. When you have duplicate parts, of course, the other advice holds; either stops or gang cutting to duplicate multiple parts which are the same exact size.

 

[zapdafish]

Funny, I was just reading up on this topic over at bridge city tools

http://www.bridgecitytools.com/blog/2010/11/02/how-close-is-close-enough/

http://www.bridgecitytools.com/blog/2010/11/08/how-close-is-close-enough-part-ii/

 

[grbmds]

The last mitered picture frame I made, I used dogs in the MFT holes to create a 45 degree "fence" and cut them using my MFT/Guide Rail setup. While I suppose there is some error, they miter joints were the tightest of any frame I've ever made. Therefore, for all practical purpose, they were perfect. I also have a clamp that is made for just the purpose of clamping frames like this. It is a 4-way clamp that tightens via a threaded bolt that brings it all together in one clamping operation. I don't know if it's the same exact clamp but a similar one is sold at Home Depot for $27 under the name Clamp-It. It has a clamping limitation as sold, but, I've merely used a longer center threaded carriage bolt in mine to make the capacity larger. I only use this as an example of the accuracy of the MFT table/Guide Rail, The TS55, and the concept of clamping all four corners together as a very accurate way of making very tight joints on a picture frame. Sort of off topic, I guess . . . Sorry.

 

[tbellemare]

The Hultafors Talmeter marking tape measures can be used like adjustable story sticks. Since they have really strong locks and marking mechanisms, all you have to do is use them to make a measurement and transfer that measurement to the work piece. It's very slick.

Tom

 

[Tim Brennan]

When I need an accurate cut, I like to use a combination square to measure and mark.

Sliding the rule up to a hard edge is far more accurate than a tape measure and far quicker.

I have this one which has a scribe too which makes a much finer mark than a pencil.http://www.amazon.co.uk/dp/B000PJAEA2/ref=pe_217191_31005151_M3_dp_1

Sometimes you can avoid needing to measure, mark and then cut accurately by cutting several pieces at once then they have a much better accuracy and it saves time. Making drawers with runners needs the sides to be  parallel and this helps with this.

 

[Ivanhoe]

Tom - those look great! never seen those before.

 

[shed9]

Most cuts don't need to be super accurate; just consistent from one to another.

Unless the finished product requires to be critically dimensioned, this about sums it up for me

 

[Birdhunter]

I have a slew of Woodpeckers and Starrett rules, squares, triangles, etc and I do use them a lot. But, mostly, I use story sticks and jigs for the high precision work I do. I upgraded my table saw from my 25 year old Unisaw to a monster Sawstop Industrial model, in part, for the extreme precision it provides.

To me, a jig allows me to get a repeatable high precision cut any time without having to do all the cuts at one time.

I like the MFT/track saw/parf dogs combination for carpentry accuracy, but the massive table saw/ jig combination is hard to beat for extreme accuracy.

 

[Jonhilgen]

By the way, here is a tip for fine trimming a board. With the miter saw off, lightly press the board sideways into the blade's teeth or plate. Then raise the blade away and make the trimming cut. If you touch the blade plate, the trimming cut will be the amount of teeth protrusion from the plate (1/2 the difference between the plate thickness and the kerf of the teeth). And the harder you press the piece into the side of the blade (before the cut of course), the more deflection of the blade and the deeper the trim will be. You can use this to nibble away as little as 0.001" or as much as 1/32" at a time if necessary.

What he said.  I do this daily when cutting prefinished cabinet trim.  It's a little OCD, but the results...

 

[Jesse Cloud]

When I "sneak up" on a cut, it usually involves a piece of paper.  For instance, first cut is between the fence and a single sheet of paper, next cut is the paper folded once, then twice, etc.  Ensures gradual work toward a snug fit without measuring.

 

[tbellemare]

When I sneak up on a cut, I turn out the lights and use my phone's flashlight function pointed at my chest with a dark shirt so the cut can't see me...

But seriously, are you talking about modifying the angle, Jesse? I like that, if you are.

The way I read Rick's post was he was modifying the length?

I just did a lot of sneaking up on cuts for trim this evening. I could have used your suggestion, Jesse. Thanks!

Tom

 

[Carl Prentiss]

When I sneak up on a cut, I turn out the lights and use my phone's flashlight function pointed at my chest with a dark shirt so the cut can't see me...
Tom

[doh]

 

[grbmds]

By the way, here is a tip for fine trimming a board. With the miter saw off, lightly press the board sideways into the blade's teeth or plate. Then raise the blade away and make the trimming cut. If you touch the blade plate, the trimming cut will be the amount of teeth protrusion from the plate (1/2 the difference between the plate thickness and the kerf of the teeth). And the harder you press the piece into the side of the blade (before the cut of course), the more deflection of the blade and the deeper the trim will be. You can use this to nibble away as little as 0.001" or as much as 1/32" at a time if necessary.

What he said.  I do this daily when cutting prefinished cabinet trim.  It's a little OCD, but the results…

Not OCD at all as it has a real point with a real justifiable result. I do the same thing  or similar with picture frames and anything that requires a precise length.

 

[Jesse Cloud]

When I sneak up on a cut, I turn out the lights and use my phone's flashlight function pointed at my chest with a dark shirt so the cut can't see me...

But seriously, are you talking about modifying the angle, Jesse? I like that, if you are.

The way I read Rick's post was he was modifying the length?

I just did a lot of sneaking up on cuts for trim this evening. I could have used your suggestion, Jesse. Thanks!

Tom

Actually, it will work for all of those.  I was thinking of putting a stop on a tablesaw sled or an mft, cutting, and if its too long still, wedge a piece of paper in.  For ripping, I would set the fence for the first try, clamp a stop next to the fence (not on the cutting side), then if needed add a piece of paper to the stop and reset the fence.

Speaking of angles, I use the paper shim on my shooting board when I'm trying to fit a drawer front to a carcass that isn't perfectly square (of course, that doesn't come up very often  ).