How much pressure is an arbour press capable of

I,m selling a large arbour press and someone has asked "what tonnage is it " so how do I calculate the pressure ? I have small one bought from Axminster almost pocket sized and they claim it's a 1 tonne size...what does that mean? My big press the gear is 25 mm radius and bar is 500 long does that mean a 20 fold increase in force applied at the handle ?making say only 2000 kg if you could apply 100 kg force?

so how do the little presses claim 1 tonne

It seems to me that mechanical advantage is the ratio of distance moved by the ram compared to distance moved by the end of the handle minus friction losses.If you weigh 100 Kg then I suppose thats the maximum possible applied force. Colin

I think the tonnage is more an estimate of how much pressure you can apply before it goes >pink< and separates into two less useful pieces. Experience of cheap cast items suggests the tonnages on the cheap ones may be optimistic.

You could work out the cross section of your column and then estimate its strengths using the UTC of cast iron, divided by a safety factor. then (and I'm not sure how) work out the ratio of the pressure to the stress in the column and compare this to what you think you might be able to generate by pulling the handle and take the lesser value.

Neil

<If you weigh 100 Kg then>

you need to go on a diet!

Some one gave me an arbour press that is labelled "1ton". the interesting thing is that the casting is splayed (arbour not at right angles to the bedplate). Any one got an idea how to remachine the bed to be at right angles to the arbour. its about 5" diam and needs a good 1mm cut right across it. The problem is that the cutter has to rotate on an arc of > 6" radius to get under the arbour bearing tube.

Frank

If you have access to early copies of MEW Ian, you will find an article of mine on using arbor presses to punch holes. They do need modifying to take out the play between ram and main body to do this though.

Briefly, the 0.5ton press was able to punch a 4mm hole, which according to calculations required about 0.5 ton pressure, but it was very heavy going.

With a longer handle fitted I was able to punch a 6mm hole (0.75 ton) with relative ease, and testing the gap in the main casting with a DTI there was no detectable sign of it opening up. The material being punched was sheet steel 1mm thick .

The article was in issue 33 page 35. Unfortunately, this is one that I have not added to my website. However, I could add a rough and ready version onto a temporary site I use should this help. I will not though be available until mid July to add any comments or to place the article on the web.

Readers may be interested, and some surprised, to learn that punches and dies will work if made using just mild steel. I have punched 10 holes in 2mm thick steel and then over a hundred in 1mm thick steel with still a little life left in both the punch and the die, It would then only be a case of returning them to the lathe and refacing them. This was of course was using a fly press not an arbor press

Harold

I should have added that the holes I punched using a fly press were 10mm diameter

Harold

Flypresses are another quandry being often referred to as No1, No2 etc,

Frank, it sounds like yours was just badly made if cast iron as CI doesn't take to well to bending. I suggest for machining the base you find someone with a shaper perhaps mounting it sideways and cutting downwards or a special L shaped extended toolholder.

Hi Ian,

You have the 2000 kg lever ratio calculation exactly right for a single action rack and pinion arbour press.

Many little 1 ton rated ones though have a toggle action rather than a rack and pinion and this toggle action can increase the press force greatly, but usually with a very short stroke.

Without some close measurement of the pin to pin distances, and some geometric calculation, the forces in toggle based machines can be tricky to calculate especially as pivot pin friction is high and there are multiple pins in the mechanism.

JD

Btw PRESSURE vs FORCE

ballerina on point weight say 40 kg (400 newtons)[ 80lb say] 1" csa = 80 psi

tank 56 000 kg tracks 6m by 1 m say {123 000 lb234 " by 39"] = 13.4 psi

Now which ould you prefer to stand on your foot ?

The ballerina... every time

She can walk all over me if she wants to

Ian

Can only think that this is a model of a 1 Tonne press. lets have a pic

Bob

Many thanks for all your replies

as I said I have a small press which is claimed to be a 1 tonne press its small weighs perhaps 6 kg and has a bar perhaps 20cm long ebays full of them

I have a very large one perhaps 75kg weight with a 50cm bar I never used it as I have a large hydraulic one which i use more so I put it up for sale on ebay ( sub sold) It was just a query from a prospective buyer as to what "tonnage" it was ...which made me think what indeed it was.as I can't imagine that the little one I have will ever provide a force of a tonne...looking at ebay ads for new chinese presses one like my big one suggests 5 tonnes for a press of this size

So how do manufacturers measure their tonnage?

Sounds like a job for the shaper to me.

Posted by frank brown on 10/06/2012 20:31:05:

"Some one gave me an arbour press that is labelled "1ton". the interesting thing is that the casting is splayed (arbour not at right angles to the bedplate). Any one got an idea how to remachine the bed to be at right angles to the arbour. its about 5" diam and needs a good 1mm cut right across it. The problem is that the cutter has to rotate on an arc of > 6" radius to get under the arbour bearing tube."

Frank, If it is the type I am thinking of, wouldn't it be easier to remove the ram cover and ram, then mill the back face of the guideway square to the base and then pack with parallel shims if required.

Regards Russ