Shopsmith Forums

I have reached the end on this thread (from my perspective). I got a few minutes to play around with my Milwaukee laser measure this afternoon. Intention was just to take a look at measuring the accuracy directly. Method was going to be taking a few measurements at varying distances from the saw blade. As a reference, I intended to use my dial indicator. By referencing one measurement to another one, I should have been able to eke out a single point accuracy estimate for the Milwaukee laser (of course this would include any inaccuracy of the dial indicator). Unfortunately, what I ran into is as follows....My Milwaukee laser measure would tend to get "stuck" on certain readings. For example, I had a reading of 8 5/16", but when I attempted to move the laser measure by 1/16" to 8 1/4" I could NEVER reach it no matter how carefully I slid it. It would always undershoot (8 9/32") or overshoot (8 7/32"). So, it is odd because it appears to have a resolution of 1/32" and clearly it does to go from a reading of 8 5/16" -> 8 9/32". The fact that I could never reach 8 1/4" seems to tell me there is a linearity problem with the measurement readout on this device. Perhaps the Bosch or other brands are better, or maybe I am seeing issues with using the sawblade as a target. Anyway, just wanted to share what I am seeing in case anyone is interested, or to spare anyone else from attempting to go down this path. I can easily move my fence 1/16", so I don't think my problem of sliding the unit was related to human error (at least not in regard to hand dexterity).

P.S. I think I kind of noticed this problem while up on the ladder measuring for my LED installation. In trying to approach a particular measurement, it would tend to jump over a measurement that I was trying to hit sometimes.

LSD means least significant DIGIT.













What were you thinking?








LSB means least significant bit(shannon)

JPG wrote:LSD means least significant DIGIT.













What were you thinking?








LSB means least significant bit(shannon)

Well you said "Digital = all bets off!(±LSD)". In digital, you would primarily talk about LSB. I have never seen LSD (term, not the drug) used in practice before, but I see now that Google has it listed. Reference to it seems to be more of a coding (SW) link. Naturally, when I saw your quote about LSD, the first thing I thought about was the common reference which is a drug, so the thought of a digital guy on LSD was humorous to me...which is why my *&^%$@ laser measure doesn't work right. I understand how you get the +LSD (drug), but how does it work to get the -LSD (take it away???)

I digress.

The "LSD" was referring to the display! The display 'displays' digits(numbers).

Ever wonder why numbers are referred to as digits?

Thanks for running this test, REGuy. This was what I was afraid with these laser measurement devices. When you are using a rule you can interpolate between graduations to estimate the reading. Evidently the algorithm use in at least some of these devices operate on a more of a absolute nature. When they advertise a plus or minus 1/16" that is what you are going to get regardless of the how it is displayed. I bet if you went to a meter/millimeter display you would see the same type of jumps.
The very best accuracy for these devices currently is plus or minus 1 mm or 1/25". When you read the fine print at least for the Dewalt 3101 it states the spec is only good for measurements less than 10 meters and can only be expected 98% of the time. I may still buy this Dewalt as a tape measure replacement because I think it is the best in the market right now but at least my expectations are set correctly.

I set up a small test bed using my woodpecker t-square and tried a few things to see how much "float" there is. I think the numbers that the manufacture gives seem reasonable but clearly it is taking its best shot at numbers down to the 1/32". Flip-flopping between +/- a 32nd if not all that bad I guess but sometimes it is a little more then that going between 3 numbers of 32nds.

Having one fixed dimension between the T and a slider gives numbers that are mostly between a 32nd when tried many times. But if you add a feeler gauge I can't seem to find a place where it locks into just one reading repeatably.

I'm going to play a little more.

Ed