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.
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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.
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?
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
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
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.
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)
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...
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 :D
Hood