Precision square - a bit of buyers remorse.

[Brian Lamb]

First post, I'll start with an introduction, my name is Brian Lamb and we make the Lamb Tool work items, the square you have been talking about in particular. I have been in woodworking for 35 years or so now, also a retired aerospace machine shop owner/operator/programmer. I have had Felder machinery since 2001 and Robland before that for maybe 5 years, I also moderate the Felder Owners Group on Yahoo, I see a few familiar names in this post.

Why I'm responding.... there seem to be some questions about accuracy. I have had the squares double checked on a CMM (Coordinate Measuring Machine) and they check within approximately .001" of square between the 16" and 24" legs, we guarantee .002" as a general rule just in case we are a few tenths of a thousandth over the .001" value. When we first started making these, I also did what one poster above mentioned, butt them back to back and run an indicator along the straight edge formed by two of them together. This is a distance of just under 48" and I have a youtube video I posted (forgive me for the lack of focus and poor video skills) and you can see the results for yourselves, that is an Interapid indicator with .0005" graduations:

https://youtu.be/kLaKDMFVmRo

In regards to the 5 sided cut, while it works pretty well and can be amazingly accurate, it is also dependent upon the operators ability to get the board located 5 times exactly correct, otherwise your final result is ruined. I used to use it and found too many times I could run the whole process 3 times in a row without moving anything and get different answers each time. That is when the idea of a large square and an indicator base became a lot easier and quicker to calibrate the fences.

If anyone has any question, feel free to ask and we will be happy to answer, or you can see the items we make, and most have PDF files on how to adjust and use them also on the website.

[marty shultz]

Wow.

I set up my Hammer B3 5 years ago, checked it last year it hadn't moved.

Are you indicating that the fence on the outrigger is coming out of adjustment or the fence on the sliding table?

regards, Rod.

No, the outrigger stays in adjustment while I keep it on the machine. However, when I take it off and replace it I like to recheck the adjustment.

[marty shultz]

What are the uses for the triangle? This may be a much less costly alternative.

No matter how much you spend for a device, you still don't know if it is square. I ran a large tool and die shop and we purchased a number of Brown & Sharp and Starrett devices and some of them were not "square". We had "standards" that our quality department periodically had validated by an outside service that we then used to verify the worker's tools.

One day, one of our designers brought in two plastic drawing triangles he had purchased at a local art supply store. He had them compared to our standards and they were as accurate as the tools could measure. The triangle cost a couple of dollars each. They would certainly serve very well as the "standard" in any woodworking shop to validate and/or adjust other devices.

An excellent way to validate the accuracy of the plastic squares is to use two squares on a flat surface. Get a $10-12 plastic 30-60-90 drafting square. To prove it's exactly 90°, take two to a glass counter, put the shorter legs on the counter and face the longer legs away from each other and butt them together (like a teepee). If the legs exactly butt, you can assume you have two perfect 90° angles. Using one of the plastic squares, do the same thing using your other tools. Any that mismatch, means that the tool is not square. You can also take the plastic square with you whenever you go to purchase another tool. Keep your "standard" somewhere where it doesn't get banged up.

Finally, remember that the wood you are using will expand and contract a couple of thousands from one day to the other. Does't pay to get too uptight.

While we are at it, I also only purchase the cheapest of adjustable squares. I square them with a drafting triangle and an auger file until they are square across 10". And I own a Bridge City square that isn't that accurate. Stainless steel machinist's squares are only square until you drop them. I have had several over the years and each has found a away to drop to the floor.

The key is to NEVER use your best square on for day to day measuring. Use it only as a reference tool to verify your other day to day tools.

In a comparison test reported in Fine Woodworking Magazine a couple of years ago, the Stanley 46-123 square was awarded the best value. It's much less expensive than a Starrett and just as accurate.

Howard, I've had similar experiences as you've had. And it upset me when I contacted Starrett to calibrate my combination square and they wanted $100!

[marty shultz]

Marty,

I have Brian's triangle. It is explicitly designed to set up sliders. So if this is your primary use case, I'd say go buy the triangle and don't look back.

I also own a smaller version of the Woodpecker's square. It does come in handy in many situations as well. 16x26 might be a bit too large for those though.

Hey Dennis, glad to hear from someone who can give first hand comments on the triangle.

I didn't say it in the original post but I want a triangle for more than just checking for perpendicularity. I also like a long straight edge to check surfaces (both flatness and co-planar). The hypotenuse of Lamb's triangle is almost 29" (if my math is right). Every extra inch is helpful when checking surfaces on the combination machines like the jointer beds and the gaps between the surfaces.



I've tried plastic before and it doesn't work as well as I'd like for situation where I need some mass when checking flatness using feeler gages.