Gallery, Projects and General > The Design Shop
Small (broach) press. Hydraulic or mechanical?
RodW:
And here is a lathe version that mounts to the toolpost
PekkaNF:
I have tried that lathe method (slide not purposemade tool) and it's ok, for aluminium and soft material but my idea of leisure gym excercise, it gets quickly laborous when key size grows and material is real steel.
I calculated some loads and power demand and it looks like minimum of 500 W of power is needed if made with trapezoidal spindles or hydraulic unit.
Cheapest seems to be mostly mechanical (two trapezoidal thread bar on tension, axial bearings, chain wheels and 500 rpm over 500w electric drill as a power unit. Also it would be a major safety issue with pretty much all parts spinning.
I'm calculating and sorting out my scrap pile of hydraulic stuff. I should have a small hydraulic unit somewhere...I only need about 2-5 cm3/r, 1500-3000 rpm pump and 0,75kW AC motor and so far I found 12V hydraulic pump, but I don't want to go there.
I'm thinkking of using a new cheap standard hydraulic cylinder (they churn out stadard parts nearby and cut/assemble cylinder lining to length. Maybe I can get one as "kit" unassembled parts for the same price? The problem here is that because I seem to be able to locate only small pumps, I need small cylinder and that's bad news on buckling load. For this application I'm thinking of using a externaly guided buffer to limit buckling.
I found one small hydraulic unit -motor and it has pump, tank, and pressure relief valve. I was hoping to use motor to reverse the cylinder by reversing the motor, but that construction will not have it. Dang. I need a manual or electric valve to reverse. The valve will probably cost the same than the surplus unit. Motor will be no problem.
I'm a little torn which way to go, both solutions have it's own set of strengths, weknesses and synergies (hydraulic unit would be great for press and some other tools).
Pekka
John Stevenson:
Out at the moment on site but I'll answer this in depth later tonight.
I do a lot of broaching from 2mm right up to 24mm and have various tools and presses, manual and power so not an expert but I have done a lot and there is a lot of things people don't fully understand about broaching.
Joules:
Look forward to that John, fed up of capsizing whilst broaching not to mention all the rust it causes on the lathe.
:palm: He who should probably be locked up.....
John Stevenson:
In no particular order and basing the reply on 6mm and 8 mm keyways.
First off what Pekka has said he wants to do cannot be done, he wants 150mm on the bed of the press and a stroke of 350mm meaning the max length of the broach is 200mm when in fact using DuMont broaches which IMHO are the best a 6mm and 8mm broach is 300 mm long. It then jumps to 353mm when you move to 10, 12 or 14mm.
Also recommended max length of cut is 63mm for the 6mm and same for the 8mm but you could have a far larger piece and still only 63mm max of keyway.
The Marlco press you linked to earlier is a two speed press and it has 400mm of daylight. I have one and they are not a nice design.
Basically the handle is the wrong way, it's not natural to pull down across yourself. It's far more natural to pull a side lever down. Plus if you have say a big pulley on the bed the handle fouls the part. Even in low speed because of the handle layout it's hard work. Mine when I got it S/H has the top mushroomed over where it had been slugged with a hammer to get a broach thru.
Next are broaching pressures which are not as high as you first think, again taking 6mm and 8mm keyways and allowing a full depth of 63mm they reckon 2,100 pound force for the 6mm and 3,680 for the 8mm but in practice you don't hit these figures. My hydraulic broaching press has a gauge on it that hardly ever gets above 2,500 on any size. Remember the bigger the broach the more passes you do so less taken off per cut.
This is my hydraulic broaching press.
It has 18" of travel and rated for 10 tonnes but never used anywhere near this pressure. If the gauge jumps above 3,00 you have problems, usually the broach has tipped and is trying to take too deeper cut. When broaching you always need to back off every couple of inches and let the work and broach come free of the ram to stop this tipping. Nice press but slow, it takes as long to return for the next pass as it does to push thru. I tend to use this on 12mm and above broaches.
My press of choice is a very old ratchet press that weights ooddles and stands outside under a sheet as room is tight. This is the best press i have for speed and power.
This isn't my press but the closest image I can find but mine has a fixed base. Because of this I'm limited to 12mm broaches because of daylight.
The cheap Chinese lever presses are useless for broaching as they do not have enough room under the ram for a broach, let alone the work. One exception is the No 4 I think it is that is a ratchet press but twice as much as the No 3 to buy.
HTH.
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