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adjusting a jump shear


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#1 dsabbagh

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Posted 21 February 2008 - 02:13 PM

The blades on a used jump shear that I bought need to be adjusted. Can somebody give me some hints on how I should space the upper and lower blades so that I can cut 20 ga. sheet? I have attached a drawing of the blades and the measurements I need. Hopefully it will be enough. If not I can photograph the actual shear.

Thanks

Attached Thumbnails

  • jump_shear.jpg


#2 KNeilson

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Posted 21 February 2008 - 03:01 PM

For my 2 cents, I would try and get a hold of the manufacturer if you could. They could give exact #`s. You will need to think of both rake(angle of blades) and clearance (spacing `tween). Also, how is adjustment made, eg, eccentrics, shims, jack bolts etc.. provide a pick and I`ll guess.................Kerry

#3 FredlyFX

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Posted 21 February 2008 - 04:26 PM

I would just trial and error it until it worked right, but I like Kerry's suggestion better.

#4 Vermontsmith

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Posted 21 February 2008 - 05:52 PM

Do you have a copy of the Machinery Handbook? I seem to recall a chart about material thickness and blade clearance ratios somewhere in there but darn if I can find it amongst the million or so other pages.

#5 KNeilson

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Posted 21 February 2008 - 06:42 PM

Let me expand a bit here. I`ll guess you can figure out the method of adjustment but need to know what to look for. This can depend on a couple things......Typically...... the more clearance, the easier the cut and the bigger the burr, up till it will fold rather than shear. The tighter the clearance the more force put on the frame of the machine. The more Rake you run, the lesser force to shear, but, too much results in "pigtailing" or curling of the material . I would adjust (for 20g) with approx .003-.005 clearance, and then try. If you are jumping on the treadle with no result increase your rake till it will cut under your weight without too much jumping. You should be able to trim 1/2" at a time off a sheet (4x8) and not get too much curling or any burrs if you do it right! I`d get the blades ground right off the bat also...........Kerry

#6 PTsideshow

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Posted 21 February 2008 - 07:35 PM

First question is it an old tool or a import knock off. If you check Harbor Frights. Foot shears(jump shears) the 52" wide one has the same set up from the US one it was copied from. pdf download able manual with full instructions for adjustment
foot shears at wholesale tool
here are east woods shears
The old diarco 36 inch shears had a blade clearance of .002 at the ends and .001 in the center you had to play with the adjusting nuts to get a clean cut. Measuring with feeler gages.
Pexto kick shears pexto shears are here made by roper whitney
They are adjusted the same way the Harbor Frights ones.
here is some more info on the pexto's with a blade pictures turn your sound off theirs is loud.
Kerry has it about right, again they are pretty much going to be one of the two styles of blades and adjusting with a number of nuts across the blade face or by two adjusting bolts nuts for the top blade etc.
[hysterical]
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#7 dsabbagh

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Posted 25 February 2008 - 04:33 PM

Hello;

Sorry it has taken me so long to respond to your inquiries. I took some photos of the jump shear. It is a very old Peck Stowe and I could not find any information at all about it. I did have the blades sharpened right off the bat. I understand the gap adjustment but I'm not sure why I would need/want to adjust the height of the bottom blade (see photo); and if I do need to adjust it, what should I look for? This whole adventure started because the shear was binding on longer cuts of about 24" (the blade length is 31"). All of my cuts on 20ga require me to stand on the treadle and jump. I need to really bounce on it for longer cuts.

Thanks for your help.

Attached Thumbnails

  • pexto_jumpshear 001.jpg
  • pexto_jumpshear 003.jpg


#8 PTsideshow

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Posted 25 February 2008 - 04:53 PM

It has been over 15 years since I was at a building that had a peck and stowe. I will look thru my collection of old sheet metal shop books and see if I can find anything. Not to sound like an ass but is that center bar and a spring in the picture. Most of the jump shears were two bars that pulled the cutting blade down from one side of the cut to the other. And sheared the sheet in two, so the top shearing blade would be on a very slight angle from the start contact side to higher at the finish of the shear side. Not to say that they didn't have a single arm pull. The treadle arms from the shear cutter bar to the foot had adjustments that were turnbuckle type and the return springs one on each side. Or is that just a return spring of the garage door type?
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#9 PTsideshow

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Posted 25 February 2008 - 05:15 PM

http://www.cincinnat..._pexto_1053.jpg

Is what I'm talking about if you can see back and under it.
another

That bar in the front on the two large screws is to hold the sheet in place while it is being sheared. And all of them I have ever used no matter what the brand or how good the blades were and adjusted. You always had to jump when they were close to the max gauge of its capacity. Hence the nickname jump shears[Smile]
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glen

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#10 dan@modernblacksmith

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Posted 25 February 2008 - 06:19 PM

my guess is that up/down adjustment is so as the blade is ground down when resharpened you can adjust it upwards so that it is flush with the bed of the machine. you can probably regrind that blade many times removing quite a bit of material and you would need to compensate for that lost material each time.
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#11 KNeilson

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Posted 25 February 2008 - 06:42 PM

I`m not too sure what to say now that Ive seen the pics. I`ll bet the jackscrews are to level the lower blade and also provide a bit of support, most machines are flush with bed (lower blade). Are the holes slotted in the upper blade? Also is there a method of jacking similar to the bottom blade, or do you just use gravity while setting it up? I`ll side with PT and bet that you are using it at close or at its capacity, hence the "jump" or lunge as you finalize your cut.
You might want to chase this down for a bit of info........
http://209.85.173.10...clnk&cd=1&gl=ca

Kerry

#12 warrent

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Posted 25 February 2008 - 09:52 PM

I have a little 30 in queen city. Best way I found to use it, is adjust the bottom blade to come as close to the top blade when the top blade is down. I find that the sliders for the top blade will give a little bit too much and your gap will open. I also adjust the top blade as much as an angle I can get, the more the merrier. I can cut 18 ga with mine. Yes I have to jump. One thing I notice on yours you do not have a hold down for your sheet. If cutting anything narrow you might want to make one up. You get some nice purple finger nails when you jump and the sheet flips up to the top blade. Experience it once and you learn quickly. And yeah those adjusters are to level the blade with the table.
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