25kn ratchet press question

[b2k]

Hi guys,
I have the press in the photo, it is rated at 25kN (around 2,5 tons of force). Do you know if it's safe to extend the lever for exterting more force? I wish to use it for clicking small pieces, like 10 or 20cm on a side. Got no problem with very small pieces (scales, lames for armors, blanks for key holders etc) but I would gladly increase the capacity for something bigger and maybe some embossing plates.

[mikesc]

I think that if you try and "click" or emboss pieces at the sizes that you suggest ( IMO 10 cm or 20 cms on a side is "not small" ) by extending the handle, you are liable to strip the teeth on the bar or the cog which drives it ( BTW..it isn't a "rachet press"..a "rachet mechanism" "locks" the "bar" after each tooth "advance"..axle stands are an example )..the press "rating" is 25kN at the downward pointing face of the bar, ( spread over the area of the bar "face" , probably around 25mm x25mm ? ) the metal of the bar ( and thus it's teeth ) and the drive cog are calculated to "not strip" at that force at that face..If you add an extension to the handle, you'll be increasing the applied force all through that "drive", but..if you are applying that force to an item that is 100mm x100mm..you have increased the area by a factor of 16..so you'll have to apply 16 times the force to the drive cog ( and the bar teeth ) via the handle to get the same pressure per 25mm x 25mm area on the item in the press..

The actual calculation is more complex than that..but the end result is likely to be that same..

IMO..you'll strip the cog and or the teeth..or break the pivot where the handle goes through the cog bar, pretty quickly.

The square section bar ( the arbor ) is usually only fairly soft mild steel ( try filing at the top of it ) , it will not hold upto more force than it is rated for for very many operations.

[Northmount]

I have a 1 ton arbour press, same design.  Used it to cut a bunch of 4" (100 mm) circles.  I slid a 3' length of 3/4" pipe over the handle to make it easier to pull down.  Rear of press was clamped to a solid bench.  Had no problems.

Tom

[mikesc]

Makes you wonder what the actual tolerances are in that case ..


Btw..those arbor presses are unavailable in France ( at anything like a reasonable price ) unless imported from the UK or Germany, despite them being made in China..The French companies that sell them at "retail" do so at 3 to 4 times the price of one from the UK or Germany, even when the international ( within the EU ) shipping of a 15Kg hunk of cast iron is included in the price.The price of a rivet setting press is just as ridiculous, and a clicker die press..ouch.

I based my "opinion" on "the calculations", however, I much prefer, ( and defer to ) northmount's real life experience with one, based upon which, I think I'll order two from Germany :)