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  1. #37
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    Quote Originally Posted by Hood View Post
    Yes, I know the type you are meaning, ones I looked at said operating range something like 0.0007 -7 Bar, so not sure how you would use them as the pressure/force would be a lot more than 7Bar.

    Maybe I am just not understanding what it means by that 7 Bar, in fact it is almost certain I am not

    Hood
    hmm strain gages wouldnt really be rated for pressure i.e. bar, theyd be rated for strain

    for instance the design steps for this sort of thing would be like this:

    -figure out for forces we are dealing with. for a drawbar force gauge id say 100lbs to lets say 3000lbs would cover pretty much anything. note that its pounds, not psi. force, not pressure.

    -select a material and diameter for the rod that will connect the pull stud to the bridge, that will handle the max tension (3000lbs) and also will develop a strain that is not beyond the capability of the strain gage you want to use to measure. typical strain gage limits are on the order of 1000 to 5000 micro strain, i.e. .005 inches per inch increase/decrease of length. so you need to do some physics/material calculations (very basic) to determine how much your bar will lengthen under the max load, and make sure its less than 0.005 inches / inch during 3000lbs (as an example). what that bar diameter and material might be is probably nothing special. id bet just off the top of my head you could use steel, aluminum, whatever, and the range of strain would just shift. i.e. steel would be a smaller range and aluminum would be a larger range because it has lesser youngs modulus and therefore stretches more under a given load.

    -now you buy your strain gage off ebay, glue it onto the rod as straight as you can, make a bridge completion circuit, connect the whole thing to a strain gage meter, and voila

    -in reality youd probably use some at least a half bridge strain gage to null temperature affects and use a gage with a tempco that matches the material of the rod. but this application is so straightforward it would pretty much work just like i described. i.e. no twisting forces and everything is pretty much in a straight line.

  2. #38
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    Thanks for the info, here is a link to the one I was looking at
    Buy Strain Gauges FORCE SENSOR I.E.E. SS-U-N-S-00015 online from RS for next day delivery.
    If you click on the product info you will see where it mentions the pressure range.

    Your explanation of how they are used cleared things up a lot for me, thanks


    I probably wont bother with using anything like this, it had sparked my interest, however when I think how little I will need to use the force gauge I think the original design with the piston and pressure gauge will do all I need.

    Hood

  3. #39
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    Quote Originally Posted by Hood View Post
    Thanks for the info, here is a link to the one I was looking at
    Buy Strain Gauges FORCE SENSOR I.E.E. SS-U-N-S-00015 online from RS for next day delivery.
    If you click on the product info you will see where it mentions the pressure range.

    Your explanation of how they are used cleared things up a lot for me, thanks


    I probably wont bother with using anything like this, it had sparked my interest, however when I think how little I will need to use the force gauge I think the original design with the piston and pressure gauge will do all I need.

    Hood
    those deeliwhoos are neat..i havent seen something like that. it probably uses a plastic of some kind that changes resistance in a non linear way with applied pressure. its not a strain gage per se really, more of a pressure sensor. i wish there was a datasheet. yes really i should be done too, but this is a perfect opportunity to try out strain gages for the first time! so more time will be wasted lol

  4. #40
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    If you click on the Product Information tab on the RS site you get a bit more info. For example:

    FSR force sensors feature an ohmic resistor whose resistive value decreases when pressure is applied. Two polymer layers are laminated together to obtain sensors less than 1 mm thick: one layer is covered with a network of electrodes and the other with a printed semi-conductor. Good measurement repeatability (±2%). Low sensitivity to noise and vibration. Service life greater than 10 million cycles. Uses: keypads, robotics, security, automotive, medical devices etc.

    Optimum pressure range 0.007 → 7 bar
    Resistance: 10 MΩ → 1 kΩ
    Maximum applied pressure: 35 bar
    Signal return time: 1 → 2 ms
    Operating temperature: -30 °C → +170 °C
    Connection: solder lugs"

  5. #41
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    It is unusual for RS Components notto have a data sheet for the things they sell but just doing a search for I.E.E. Technologies and Force sensor brought up some hits. I have not looked further but you may find some info.

    Hood

  6. #42
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    Well I got a chance to test out the gauge by using my weight and it works out fine, the gauge showed somewhere between 600 and 650 PSI. I weigh 95Kg so 95 x 2.2 x 3 = 627Lbs so 627PSI is what I should have got and did get approx that.
    Hood

  7. #43
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    Quote Originally Posted by Hood View Post
    Well I got a chance to test out the gauge by using my weight and it works out fine, the gauge showed somewhere between 600 and 650 PSI. I weigh 95Kg so 95 x 2.2 x 3 = 627Lbs so 627PSI is what I should have got and did get approx that.
    Hood
    id be interested in hearing what you find out about your drawbar having low force...i wonder whats up? mine was also very very low..maybe 120 pounds force! the springs all looked good but i dont know if they were worn out or made of very inferior materials (far worse than mcmaster carbon steel)

  8. #44
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    The bad thing is I do not have a clue regarding my drawbar. I have been unable so far to find any information about it and no one seems to know how to dismantle the spindle to get access to things. I dont even know how to get the spindle out of the head. I have seen some information about Chiron FZ spindles but all seem to be a bit different and none really look like mine. The drawbar is deep within the spindle itself so I think I will just have to bite the bullet one day and go in blind and try and see how to dismantle it.

    Hood

  9. #45
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    Nice to see others benefiting from this design. Sorry acannell for not posting back sooner. I have been so busy I just have not had 5 minuets to myself. Hey Hood. I take it your the same Hood over in the mach3 forums? Nice to see your interest in this. Nice work on the build. Someday maybe I will finish that lathe screen huh?

  10. #46
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    Yes, same Hood.
    Wouldnt bother too much about your screen if you dont use Mach now, if you come back to Mach when Mach4 comes out you will likely have to redo anyway as VB wont be use any more.
    Hood

  11. #47
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    Hopefully Mach4 will be better than Mach3 was on the lathe side. I had some serious surprises a couple of times that made me switch to Linuxcnc out of safety concerns. Oh and rigid tapping was sure a great bonus

  12. #48
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    Never had any issues myself with Mach3 Turn, yes there are things it doesnt do well or at all but nothing that has caused safety issues for me. What was it that gave you problems?
    Regarding rigid tapping, never done that on the lathe as any threading I do is bigger stuff but do it all the time on the Chiron FZ12.

    Hood

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