Arbor Press Force Gauge?
Has anyone rigged up a pressure/force gauge on their manual arbor press that is capable of giving a pressure/force reading with each stroke of the ram? I just like the idea and have been thinking on this for a few years after seeing how Dake uses a PSI gauge on their hydraulic press models. What could be used for a similar pressure/force gauge on a manual 12 ton press, which obviously doesn't have existing hydraulic lines to hook up to?
Obviously, the more accurate the device, the better, but would such a device be used to read in "tons", "lbs" or ???
How do the Dake hydraulic gauges read? How are they graduated?
You could wire a strain gain to the end of the ram, with an tool steel tip protecting it. Or have the strain gauge underneath the pressure plate that supports the workpiece.
I've wanted for years to do this to my old Weaver 20-ton screw press
I have three ideas.
1. Strain gage. Needs power supply, signal conditioning, calibration
2. Some sort of hydraulic "pot" under the workpiece, and a pressure gage. It would get in the way of most of the jobs I do
3. A mechanical "strain gage", ie a system of levers to amplify the elastic deflection of the pres frame. It would end up moving a pointer on a dial. Even on the simple H-frame of my presss, where one MIGHT ASSUME fairly uniform stress distribution, (approx 5 sqin metal in the siderails of the press in tension, 20 tons should stretch them by approx .0002 in/in.)
So, if I clamped one end of a 10" rod alongside the rail of my press, and mounted a "tenths" indicator to read the other end of the rod, each ton should very roughly read as a ten-thousandth of an inch.
I have not tried this, 'though it has been great fun to think it through (Thanks!). I think non-uniformities of stress-distribution would probbaly mess this simple mental exercise up badly. And if you are talking about a c-frame rack-and-pinion press, calculating the deflection at any given radius from the web would be very dicey. If you used a hydraulic cylinder with gage in the press to plot an empirical calibration curve, I think you might end up with something useful..
I make a small hydraulic press and use a torque wrench as a way to gauge pressure you might be able to attach one to the arbor press and figure out the tonnage. I cut the end off of them and weld on a straight shaft.
Calculate the mechanical advantage, and rather than measure the force directly at the ram, estimate force applied at the lever.
I made this for custom preloading spindle bearings using an arbor press, and for setting a torque limiting machine vise. It has many uses, and accurate.
A hydraulic scale, the ram is exactly one square inch. Any range of gauge can be used with it.
A 400 lb gauge in the photo, I have used it to 12000LB with a 15000LB gauge.
It will attach to the ram.
Hydraulic scale picture by donsmonarch10ee - Photobucket
A 1.125 inch cylinder will read directly in psi/pounds, since a 1 1/8 cylinder is exactly 1 square inch. [.9940]
If a 1.125 inch pancake cylinder existed, with adequate psi rating, it would be a simple matter of hooking it up with a proper gauge, and installing it at the base of the force.
Load cells are nice, also.
And ebay has them
NEW Honeywell Load Cell 150000 lbs Range 15-26VDC 73A - eBay (item 310224324438 end time Sep-30-10 07:59:40 PDT)
When it comes to load cells, some allow tensile operation, beside compression.
NEW Honeywell Load Cell 150000 lbs Range 15-26VDC 73A
From our online store inventory, we are selling a NEW Honeywell Load Cell.
Model #: 73A
Range: 150000 lbs
Supply: 15-26 VDC
Output: 0-10 VDC
Which would allow a threaded rod at one end of the anvil to be suspended off of its adjustment pin, just enough for the cell to take the force. Whether you sum the output of multiple cells, or use a scalar adjustment for the leverage is up to you.
100,000 Newtons is about 20,000 lbs, so you could have a Newtons scale, to confuse the onlookers.
Hey magneticanomly, I just bought one of these Weaver presses this past weekend at an estate sale. Paid $25 for it. Looks like it may be missing some sort of handle mechanism to assist in turning the handwheel.
Could I get you to post a couple of photos of yours so that I can see what I am missing?
Here is an overall picture of the press, and one of the mechanism that perhaps you are missing. I dunno how to put the pic in the text (maybe someone will tell us), so it is a thumbnail below
If you need more details let me know. I'd be glad to make dimensioned sketches, if you need to make pieces
I actually have wanted for years to replace the lever with a large wheel and a crankshaft, so that I can drive the ratchet mechanism with a rotary motion
Sorry for the distracting background. The press is set up in my "Indian garage", excellent ventilation and lighting (during the day) but poor climate control
I think I have only seen two of these presses. The other had a lot of wear and chipping on the teeth of the nut/wheel, which might have let the pawl slip. I suppose a wheel with such damage could be welded up and dressed-out.
They have a very interesting mechanism for quick-release, a pair of helical washers between the upper (thrust) face of the nut and the counterface. A torsion spring is supposed to keep these washers turned to the expanded position. When you try to turn the handwheel backwards, they collapse, unloading the screw.
I made the mistake early in my ownership of the press of lubing those helical faces with never-seez, which made them so slippery that they collapse together and fail to function. I am very happy with my moly lube on the screw, but some day I need to take the whole thing apart, wash those helical faces off with gasoline, and relube them with plain light oil.
Last edited by magneticanomaly; 10-21-2010 at 07:10 AM.
Reason: add photos
I like screw presses better than hydraulic. I have used a 35 ton simplex mechanical screw jack in a simple H frame press for decades. I've always been pleased with how well the screw jack performs compared to a similiar capacity hydraulic system.
Why not just make the handle into an old-fashioned, 'child's play'- simple torque wrench, with a curved scale and a long pointer measuring the deflection over the length of the handle shaft?
You could either calibrate against a torque or weight standard, or calculate the cantilever deflection, using WL^3/EI times a fractional term, found in the likes of Machinery's Handbook
I like donie's solution best. (Nice Starrett No. 21 square there donie) It is basically the same setup I have on my hydraulic press which is an old Cutter Lab Press. The gage also has a moveable hand that tracks max pressure. This brings up a problem with most solutions... how much pressure is actually applied?
Typically when pressing something into something else, say a short cylinder in to a slightly longer cylinder the pressure gage will read quite high just to get it started. The pressed in part starts to move and the pressure drops. You give the handle another stroke and the pressure goes up again (though usually not as high), the part moves and the pressure drops... and so on. As the pressed in part gets deeper into the bore the "make it move pressure" (static friction) goes up for each stroke. The "as it moves pressure" (dynamic friction), though still lower than "make it move pressure", will also increase. Finally you bottom out and each additional stroke just increases the pressure with no additional movement of one part in to the other.
This is similar to torquing a bolt.
What is it you want to measure? Is there some limit that must not be exceeded? Is there a max final pressure that must be reached?
For most stuff I would prefer donie's analog method. Next up would be the torque wrench method though probably not as accurate as a direct reading pressure gage. Then a load cell... costs a bit but it can be hooked to some recording device or whatever. I have various load cells I use around the lab that hook up to a computer and will give me a graph of the pressure applied vs time or vs distance.