$100 chinese 4" vise deflection + DIY force gauge

[spaceman_spiff]

So I got sick of my part coming out wrong in the Y axis as far as not syncing surfaces up when flipped over in the vise and simply geometry being in the wrong place, so I decided to measure my vise deflection. Turns out its moving quite a bit, enough to explain what I'm seeing I believe.

The tools I used in the test:

-harbor freight in. lbs. torque wrench
-harbor freight ft. lbs. torque wrench
-homemade drawbar force gauge being used to measure clamping force
-Mitutoyo 0.0001" test indicator

I took the deflection from two spots, one right above the fixed jaw on the drawbar force gauge block which was in the vise, and the other, right on the top rear of the fixed jaw. Obviously the torque wrenches arent exactly NIST grade, but I'm pretty sure the force gauge is accurate. Regardless, everything is accurate enough to get a good enough idea what is going on. When I did the back-of-jaw data, I slid the force gauge over so its piston was centered in the vise.

After I did all the tests, I closed my eyes and tightened the vise to what I usually tighten it to (damn tight until I'd need to do a push up on it to get it any tighter)..the PSI went OFF THE GAUGE. Meaning Probably 3000+ lbs of force. I'm pretty sure thats overkill for the work I've been doing.

I've seen two interesting web sites about tuning up the cheaper vises. Neither one seems to offer any before/after data on deflection though.

Enco Vise Tune-up

Fixing the 4 inch mill vise

Before I did these tests, I took the fixed jaw off to see whats up. Didn't find anything shocking. I just filed lightly to remove any burs and put it back together. I replaced the two 8.8 grade bolts with 12.9 bolts and torqued them to 29 ft lbs (apparently the max. recommended). I found that they could be a bit longer too. there is a good 0.3" of thread left in the fixed jaw once they are tight. So I'll get some longer ones and maybe it will help a little. I might also explore upgrading the bolt size to bigger, like one of those threads shows, but I dont have another vise so I might run into trouble using my mill to do the work.

I am not badmouthing this cheap-o vise. It was about $100 from some no name ebay seller about a year ago. Its been my workhorse and has taken me VERY far. And from what I read about kurt vises, deflection of this sort is still a reality even with those. I'm not sure what the kurt 4" deflection vs. force relationship is, but its not a horizontal line.

EPILOGUE:

I have now started using a $9 horrible freight torque wrench to tighten the vise during my setups, and only use the standard vise handle for loosening the vise or if I need to move the vise jaws a large distance and take advantage of its U joint.

The torque wrench lets me create consistent and proper clamp loads, which reduce vise deflection and make the accuracy and repeatability of my setups go way up. Its a major improvement. Alot of my work involves multiple vise-aligned setups where the tilt of the part in the vise cant be easily compensated for by zeroing off a particular machined location.

I'm not sure how much these tests indicate the quality of the vise either way, or how much they would improve with a more expensive vise. All vises deflect. Kurt does make a 4" vise with a one-piece fixed jaw (no key or bolts), which would surely have better deflection, but its $1100. I think in this case, as usual, proper setup and planning can equal or exceed counting on superior specifications of better equipment.

Now if you were doing a cut that needed 3000 lbs of clamping and had to be aligned within 1 thou when it was flipped over, blind, the vise accuracy may play a more important role. But for small machines with lower clamp load requirements, a more rubbery vise can probably get the job done if used properly.










[/QUOTE]

 

[JimDawson]

Re: $100 chinese 4" vise deflection data

Very cool setup, and good write up. Would you provide some details on your force gauge? That looks like a useful tool.

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

Very cool setup, and good write up. Would you provide some details on your force gauge? That looks like a useful tool.

Thanks, the force gauge is indeed a useful tool to make, and its simple too.

Its exactly what it looks like, a piston with an o-ring that rides inside a blind hole (cylinder) in a block.

Then you add a small passage to the cylinder for the pressure gauge.

I just filled mine with water, perhaps hydraulic fluid would be more appropriate. You need to bleed the air out of it somehow so there is nearly no movement of the piston when compressed.

I'm not completely sure but I believe you could use old welding gas pressure gauges for this..a cheap source most people might have laying around the shop.

In effect its just a hydraulic force gauge.

To make it specific to measuring your drawbar force you need to figure out a way where the drawbar ends up compressing the piston somehow.

The oring groove and cylinder size are all designed using standad oring gland tables found all over the internet.

Make sure to do a little pre-planning to make sure the forces you expect to measure will show up on the gauge you use, accounting for the cylinder diameter you select.

 

[Andre]

Re: $100 chinese 4" vise deflection data

What a cool force gauge, I just so happen to have a 3600 PSI pressure gauge lying around (no joke) and now I have a use for it! I will probably use a bore that measures one square inch. Looks like I'm going to have to find a .5641895835477563" reamer :rofl:

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

What a cool force gauge, I just so happen to have a 3600 PSI pressure gauge lying around (no joke) and now I have a use for it! I will probably use a bore that measures one square inch. Looks like I'm going to have to find a .5641895835477563" reamer :rofl:

be sure to post pics when you do!! of the reamer and the force gauge you make lol

 

[JimDawson]

Re: $100 chinese 4" vise deflection data

What a cool force gauge, I just so happen to have a 3600 PSI pressure gauge lying around (no joke) and now I have a use for it! I will probably use a bore that measures one square inch. Looks like I'm going to have to find a .5641895835477563" reamer :rofl:

You might want to use a 1.1283791670955125738961589031215 reamer, it's a bit closer to 1 in[SUP]2[/SUP]

 

[Glenn_ca]

Re: $100 chinese 4" vise deflection data

Why be concerned with the size of the hole since you are measuring total force not force per square inch.

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

Why be concerned with the size of the hole since you are measuring total force not force per square inch.

itd be nice so your gauge reads directly in lbs force instead of requiring arithmetic ..otherwise doesnt matter really as long as the force and piston size will show up on the gauge psi for whatever force range you expect to encounter

 

[Glenn_ca]

Re: $100 chinese 4" vise deflection data

itd be nice so your gauge reads directly in lbs force instead of requiring arithmetic ..otherwise doesnt matter really as long as the force and piston size will show up on the gauge psi for whatever force range you expect to encounter

Regardless of the size of the hole the indicated pressure will be the same and is the pressure being exerted on the vise. To determine the psi you need to divide by the area within the jaws.

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

Regardless of the size of the hole the indicated pressure will be the same and is the pressure being exerted on the vise. To determine the psi you need to divide by the area within the jaws.

not really..

say your piston is 1 square inch

and you put 1 lb on it

your gauge will read 1 pound per square inch (convenient)

now say the piston is 10 square inches

and you put 1 lb on it

now the gauge reads 0.1 psi (do some multiplication)

now just replace "you put x lb on it" with "the vice exerts x lbs clamp force on it"

the area within the jaws is irrelevant because it translates into the same force on the piston, regardless of how much of the piston is inside the jaws. If the entire piston isnt within the jaws thats not good for this simple design, because the piston will tilt to the side and probably not work right, but for discussions sake, it doesnt matter, because whatever force you are exerting on the piston does not depend on how much of the piston you put it on.

Kind of like how your bathroom scale doesnt care how big your feet are, or if you decided to balance yourself on a soda can on top of the bathroom scale..youd get the same weight (plus the soda can).

are you sure we're talking about the same thing?