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  1. #21
    Join Date
    Oct 2004
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    832
    Ha ha yes just to get the effective area of the piston


    The pullstud/taper were tight and dont think there would be any air pockets as I filled from the gauge end and had to bleed off pressure to get the needle to zero.
    Regarding the pullstud being pulled out, I would imagine it has to be or there would be no compression of the piston.

    I will see if I can work out a way to test the setup, should be relatively easy if I can get something of known weight, suppose really all I need is something around about 200Lbs to see if the gauge shows the same as it did in the spindle.

    Hood

  2. #22
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    Dec 2012
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    Quote Originally Posted by Hood View Post
    Ha ha yes just to get the effective area of the piston


    The pullstud/taper were tight and dont think there would be any air pockets as I filled from the gauge end and had to bleed off pressure to get the needle to zero.
    Regarding the pullstud being pulled out, I would imagine it has to be or there would be no compression of the piston.

    I will see if I can work out a way to test the setup, should be relatively easy if I can get something of known weight, suppose really all I need is something around about 200Lbs to see if the gauge shows the same as it did in the spindle.

    Hood

    ill try to get something up too.

    as far as the pull stud moving, if we made the system totally free of air, then we can assume the hydraulic fluid or water is incompressible (or nearly so) and then the displacement becomes very very small, i.e. essentially a solid..we dont want the pullstud coming out a significant amount, because the more it comes out, the less force is on it (via the spring constant). i suppose if the overall spring constant of the stack is something like 500 lbs/inch (like mine should be) then every 1mm is 19lbs less of force..but my stack is 48 springs and is about 80mm long and undergoes about 11mm of deflection with a tool in it. but on a tormach, for instance, where you have 8 much thicker springs and the spring constant of the stack is much much higher, 1mm could end up being hundreds of pounds so in that case displacement of the pullstud is much less desireable

  3. #23
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    Oct 2004
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    832
    It would be easy to see how much the stud gets pulled out of the holder, just need to measure before and after of the piston from the cylinder, the difference will be the amount the stud has pulled out of the holder.
    I will have to check the gauge length of the taper I made up with respect to a proper tool, I wasnt too particular with that and I suppose it could be having an affect, especially if I had it too long.
    I cant remember how many bellevilles were on the Beaver, seem to think 112 but would have to look back and see to be sure.

    Hood

  4. #24
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    Oct 2004
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    832
    Just looked to see how a pressure gauge actually works and now I see there should be minimal movement of the piston. I was thinking there was some sort of piston inside the gauge that moved thus allowing fluid to enter but I see now that the way it works is there is a tube inside with a coiled section, as the pressure increases then the coil tries to straighten and thus the needle moves (via a linkage), so no extra fluid will enter the gauge.
    Will see if I get time tomorrow to rig something up to test, I have plenty of heavy stuff lying around, just dont know its weight, should however be able to weigh something as the Fishermen have digital scales for weighing their lobsters so I will see if I can borrow them

    Hood

  5. #25
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    Apr 2013
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    1788
    Don't you have a bathroom scale? How about attaching the pull stud to something overhead and supporting your own weight by the outside cylinder? If you're my size that should give about a 200 lb weight.

  6. #26
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    Dec 2012
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    Quote Originally Posted by kstrauss View Post
    Don't you have a bathroom scale? How about attaching the pull stud to something overhead and supporting your own weight by the outside cylinder? If you're my size that should give about a 200 lb weight.
    that would probably work, but you'd grab it by the taper not the cylinder, in order to simulate its action in a spindle. need some way to grab the pullstud too..

  7. #27
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    Oct 2004
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    832
    Ok bit of an update, not managed to actually test things with weights and need to get on with work and some clearing (newish band saw arriving today and need to make space) but I measured the gauge length and it was a bit too long. Machined the end of the taper section and then the same amount off of the rod that the pullstud screws into. Assembled again, filling with excess oil and bled off the excess pressure as I tightened the pullstud. Put in spindle and was a bit happier to see the pressure now at almost 1200PSI. That means its still only about 400 lb-f on drawbar but its a 100% improvement over previous test.
    I will hopefully get a chance to do a test today with a known weight (kstrauss, good idea I know how heavy I am (read fat ba$ard at 95Kg)) so will bore a hole in a flat bar and pass the rod through it. Will take off the taper so that the piston rests on the flat bar then place the flat bar on my press table, facing down, and finally screw in a stud with a foot hold welded to it. I will then stand in the foot hold and that should let me see how the gauge reacts.

    Anyway heres a couple more pics of my setup, now I realise that the piston does not move much due to the construction of the gauge I could reduce the bore length for the piston, in turn that would reduce the amount that I needed for the larger dia going into and overall I could reduce the length by probably 40mm.

    Hood

  8. #28
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    Dec 2012
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    Quote Originally Posted by Hood View Post
    Ok bit of an update, not managed to actually test things with weights and need to get on with work and some clearing (newish band saw arriving today and need to make space) but I measured the gauge length and it was a bit too long. Machined the end of the taper section and then the same amount off of the rod that the pullstud screws into. Assembled again, filling with excess oil and bled off the excess pressure as I tightened the pullstud. Put in spindle and was a bit happier to see the pressure now at almost 1200PSI. That means its still only about 400 lb-f on drawbar but its a 100% improvement over previous test.
    I will hopefully get a chance to do a test today with a known weight (kstrauss, good idea I know how heavy I am (read fat ba$ard at 95Kg)) so will bore a hole in a flat bar and pass the rod through it. Will take off the taper so that the piston rests on the flat bar then place the flat bar on my press table, facing down, and finally screw in a stud with a foot hold welded to it. I will then stand in the foot hold and that should let me see how the gauge reacts.

    Anyway heres a couple more pics of my setup, now I realise that the piston does not move much due to the construction of the gauge I could reduce the bore length for the piston, in turn that would reduce the amount that I needed for the larger dia going into and overall I could reduce the length by probably 40mm.

    Hood
    just so i understand, the longer taper made the force read lower because it meant the pullstud was further up than it should be, which created a gap between the pull stud gripper and the pullstud, which reduced the spring stack compression when the drawbar puller pulled?

  9. #29
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    Oct 2004
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    832
    The taper being longer meant the pullstud was higher up and this allowed the part that grabs the pullstud to bottom out against its stop and thus the force exerted was not the full amount.
    Make the gauge length correct meant that the taper was fully seated in the spindle taper and there was still a gap between the grabber and its stop and thus the springs were exerting full force on the pull stud.

    Still not too happy with the force I have but its definitely better, I will however try and find some info on the makeup of my spindle/drawbar assembly and if I can find info on it I will likely see if I can get it better.

    Hood

  10. #30
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    Oct 2004
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    832
    Also I should add, the tool holders in my machine are a bit different than standard BT or CAT 30 holders in that they are a bit shorter.
    Never had time to test out the gauge by using my bulk and will be working away from the workshop over the next week so likely wont get a chance. I am fairly confident now however that it is working as it should.
    I probably spent around 3hrs making it so it is well worth doing when comparing to the cost of the commercially available ones and I am glad I saw this post

    Hood

  11. #31
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    Jun 2008
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    1082
    This is a cool idea! I'm going to try to make one myself, eventually. I'll be sure to post here when (and if) I build something that works.

  12. #32
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    Quote Originally Posted by Hirudin View Post
    This is a cool idea! I'm going to try to make one myself, eventually. I'll be sure to post here when (and if) I build something that works.
    awesome i cant wait to see it!

    btw it turns out there are companies that make drawbar force gauges that are completely wireless and get held in the toolchanger just like a tool. so you can just switch to the force gauge "tool" and then have the force wirelessly sent somewhere, for frequent checking of drawbar force. this would be cool to make! kind of ridiculous for my particular mini mill with a 6 tool ATC, but for someone with a bigger mill with lots of tool space and/or someone who really pushes their machine hard with toolchanges, making a wireless version with a pressure sensor and electronics could be fun.

    im just getting into strain gauges, so i think for a fun project I will try to make a strain gauge version of this. its pretty much perfect for it since you can put the strain gauge on the rod that connects the pull stud and bridge, and the forces will likely only be in one direction so there is a lot less to worry about as far as nulling things.

  13. #33
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    Oct 2004
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    832
    Hirudin
    Will be good to see another one
    I know I will do mine slightly different the next time but it will be similar in that I will have the taper sleeve, that way I can use the 30 taper sleeve for the Chiron and then make a 40 taper sleeve for the Beaver, will just need a longer thread on the pullstud.

    acannell
    Got any links to these straing gauges, few I looked at before were only about 7Bar if I recall.

    Hood

  14. #34
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    Dec 2012
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    Quote Originally Posted by Hood View Post
    Hirudin
    Will be good to see another one
    I know I will do mine slightly different the next time but it will be similar in that I will have the taper sleeve, that way I can use the 30 taper sleeve for the Chiron and then make a 40 taper sleeve for the Beaver, will just need a longer thread on the pullstud.

    acannell
    Got any links to these straing gauges, few I looked at before were only about 7Bar if I recall.

    Hood
    by strain gauges i meant more the actual elements that get glued to materials in order to literally measure strain. they look like teeny little zig zags and cant be used by themselves, they need a completion bridge usually and sensitive electronics, all of which are off the shelf items, but its not unless you get lucky and find a bar of metal with the right kind of gauge already glued to it, you are starting from scratch. but im playing around with them at the moment so im willing to deal with all that to get something going. it might be much easier to just buy an off-the-shelf pressure sensor with a voltage output. three wires, power, gnd, output. then you just need a voltmeter and voila electronic drawbar force gauge. but strain gauges literally measure the strain of the metal..i.e. like .00001" stretch with 100lbs on 1" diameter 6061 (just made that up but its close)

  15. #35
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    Apr 2013
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    An earlier poster wondered about the internals of commercial units. See https://www.google.ca/patents/US6533507 for one patented device. Looks rather like a Clamprite...

  16. #36
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    Oct 2004
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    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

  17. #37
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    Dec 2012
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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.

  18. #38
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    Oct 2004
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    832
    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

  19. #39
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    Dec 2012
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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

  20. #40
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    Apr 2013
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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"

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