Idea for product (T Square with moveable distance measurement module)

[cliffp]

I have not yet found the perfect solution to measuring or marking wood where I want the distance to be along an axis that is accurately orthogonal to an edge (I know this is what all of us want to do routinely!).

At the moment, I use my Woodpecker 600m square to get the 90 degrees, line a 1 meter ruler against it, use an engineers square to align the end of the ruler against the edge of the wood and mark with a good marking knife (using reading glasses). Apart from the palaver, it is difficult to judge fractions of a mm.  I like the idea of a T Square (such as Woodpecker's) but this would not (I imagine) easily permit measurements/marking sub mm.

It occurred to me that if you could make a T square in which the measurement limb (the long part) did not have a detailed scale but instead had detents so that a moveable carriage could be precisely slid along it and engaged with it (a bit like the LR32 plate the router is mounted to) at different locations. These locations could be 100mm (metric) or 4" (imperial). For a DIY'er, the increments could be 32mm using the LR32 system. This carriage would have to be made such that it fitted precisely so that its axis was always aligned with the T square arm.

If components from a digital height gauge such as the one shown below (with indicated parts removed) were attached to the carriage and this assembly mounted to the T square long limb at precisely defined points, the gauge would enable accurate and easily accomplished measurements/marks within that range (typically 100 or 150mm). If we arranged our detents such that it was possible to zero the height gauge when the measurement edge (as indicated with an arrow in the photo) was aligned with the edge of the wood and the other detents were at 100mm, 4" or 32mm (depending on our chosen measurement system) intervals, we could add this offset to the gauge reading for the overall measurement. The gauge head could be locked down so that if we chose to set a distance we wanted to transfer onto several workpieces we could. 

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[MetalDemigod]

I for all argumentative purposes  am just an average woodworker, but between products Festool, Incra, woodpecker and fast cap (had to include them) I can make accurate repeatable cuts well sub .003'. I have read .008' is considered acceptable for woodworking. We all try our best, .... And when we fall a bit, short... Hope our "quest for perfection" put us at an acceptable tolerance. I'm not saying a better solution Isn't out there, and hell, I'd love to me the way be the one to come up with it. But remember, .001 IS NOT the end of the line for tolerance. Thier is always .0001 and beyond. I've seen "high dollar" automated positioning machines, but for what woodworkers do, (especially us garage ones) why? I love toys and like to have the best of what I can afford, so if something awesome comes out to improve my time or accuracy, I would definitely give it the time of day. But I am very content with the options available to day.

Ps. If u don't know about incra look at the LS poitionser. They advertise.003 I believe, but I assure you my tS is getting .001.

 

[cliffp]

MetalDemigod, thanks for the feedback. I will look into the various Incra products and see if other products would meet my as yet unmet need. I have their 12" rule and find it very useful for (relatively) short measurements but I don't find it ideal for use with a marking knife. I know that there are machines that can achieve far better than the 0.1mm or so accuracy I am hoping to achieve but I don't feel that this level of accuracy is necessary. The fact that it is achievable merely makes it easier to manufacture a hobbiest level product that would be accurate to say 0.1mm.

I may either make a prototype (technology demonstrator) using wood and the LR32 system or I may get my engineering workshop to make a prototype using aluminium or steel (I work in a University Engineering department).

 

[Bohdan]

Years ago when I needed to setup production machinery very accurately I purchased a 1 metre long vernier. This would enable settings to 0.1 mm over a distance of 1 metre to be easily achieved. It also became the factory standard against which all other scales were tested and quickly showed that most commercial rulers and even some of the machine scales were not that accurate and could not be relied on.

The timber stability was another issue, readings taken one day did not match those taken several days later but as I was working with chipboard the expansion and contraction of the pieces cancelled if they had originally been machined at the same time.

This was possible in a production environment but that sort of accuracy is unlikely to be of much use when different parts are machined over a period of several days or you are working with solid timber. These days I prefer to rely on the old finger test to see if two parts match for length and a shorter vernier to set up depths and widths when grooving.

 

[cliffp]

Bohdan, thanks for that - a very interesting insight. Although a lot of what you said is (or ought to be) obvious to a woodworker with a reasonable amount of experience (albeit hobbiest), it is easy to forget things that we have observed and not realise that for example expansion and contraction of mdf or chipboard would affect all parts equally.