Gallery, Projects and General > The Design Shop

Small (broach) press. Hydraulic or mechanical?

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lordedmond:
Thanks John lots of info for a Ilson lad to take in :)


Stuart

PekkaNF:
Thank you very much. I'm pretty confident that that I'm not the only one who is happy with your input.

I really appreciate opinion that is based on plenty of experience and though.

Also those load figures are really appreciated. I had only some table values to go.

I may have worded wrongly work envelope (based on next machines and a lot of questimate):
* Max gear/boss/bush/sprocket diameter 150 mm.
* Daylight to accept 6/8 mm broaches, which seem to be pretty much 300 mm in length + some provision for parts
* Rest of it I needed feedback and started this thread.

I had some junk I thought I might be able to use. Like the 4t jack, pump and works. And although I made a sketch which would allow to use it (even with limited stroke) standard spacers would nesseciate four pittstops.

I may have a little obtuse entry angle to this topic, but my starting point is that broaching key way is not that different from any other type of machining (tooth loads, cutting forces etc.) EXCEPT that an internal broach has very limited chip space and cutting speed is usually low.

I had some table cutting forces to go and concluded fast that relatively much force is need to push or pull the broach trough a piece of metal. That translates pretty big trapezoidal screw (specially if in compression), fairly big losses and needs some attention to bearings etc. Then again same force could be easily done with very modest hydraulic cylinder, only real limiting factor seems to buckling of the rod if in compression.

With this reliable data and opinion I'll calculate and sketch a little more and then I'm whole lot more confident to make my decision.

Pekka

John Stevenson:
Pekka,
I know you are not doing this commercially but bear in mind time taken with screw or hydraulic press to do a keyway.
The DuMont broaches are the best 6mm requires 2 passes, one from scratch and then a shim added. 8 mm requires 3 passes and 2 shims.

However some broaches out there like the Marlco range require far many more passes from memory their 8mm broach which in all fairness is a bit shorter requires 8 passes. If you have say 10 sprockets to keyway there is a big different between 30 passes and 80 passes.

When I first started off in a tiny shed restoring racing bikes I built a small 20 ton hydraulic press for doing flywheels. I then started to use this to do 1/8" keyways in timing gears with a Marlco 4 pass broach and soon gave this up as an exercise in futility.

So I then scrounged a length of rack, bolted two steel side cheeks to it with countersunk screws and a packing piece in behind the rack so in effect I had a 2" square steel bar with teeth on it as a ram. Then just drove this with a gear and capstan type handle.

The whole arrangement was mounted on the hydraulic press at the side of the ram so I had the best of both worlds.

I then bought a DuMont 2 pass broach and that made things a lot easier.

Using a rack and pinion also gives you feel, hydraulic doesn't and if it wasn't for the pressure gauge on the big press I wouldn't know if the broach had tipped and was ploughing a deeper keyway than needed and also the fear of shattering a broach.

PekkaNF:
I hear what you are saying.

I have done one keyseat on lathe (and something similiar) and it was not a pickinik even with a single tooth cut....now increase DOC and two more tooth, and soon it will be chore.

This trapezoidal screw application was to be fitted with 0,55kW worm gear AC-motor. Secondary speed 100rpm, other 0,75 kW 140 rpm. Right on money but both had a hollow shaft of only 25 mm ID and bearings would not take the load. Calculated that it would just do close to 20kN with 7mm/s feed, but it would have two lead screws on compression, three or four chain wheels etc. Something that would make H&S cry. But the parts that I need to buy would amount about 150€

Then I calculated the whole cacadoodle with a small hydraulic ram and small/cheap hydraulic unit (that sadly has no motor) and it would do with standard parts 6kN of linear force and 7-9 sec of push and about 5 sec of pull. Pressure meter would be not overly difficult to add and I have some experience on hydraulic units. Good news is that frame would be easier to make than on mechanical press and I have all the metal.

I located small surplus hydraulic unit sans motor on 70€ and it is only 40 km one way.... :) Ram would be easy there is a shop that would sell me "kit"on 120€, but hand valve is 90-120€ and B14 frame 71 motor is about 150€ and some money on hoses and quick disconnects would frigging doubling the cost! :bang:

Going electrohydraulic has some benefits and I could use it for a shop press (whole lot more force, but smaller stroke and speed) when I need one, but probably I could do fine without that much ado. Can't really build first the manual and then "upgrade" it to hydraulic unit, because handpump I have has even lower volume and it would take ages to move this ram.

Now, I equally dislike having too limited tools or going overboard, finding a middleground with my lack of expertice is hard.

Pekka

Aargh.

Manxmodder:
Pekka, in my younger days I have worked on large industrial hydraulic pull through broachers cutting hexagonal profiles,squares and large keyways.

I have also had quite a bit of experience using smaller broaches on an arbor press.
 
What John Stevenson says about needing to feel a broach that is being pushed is absolutely right,and I firmly believe an arbor press is the best choice for push broaching.

Hydraulic press push broaching can be hazardous and expensive if the broach shatters,so I would always look to pull broach with a hydraulic setup.

In the final analyses what John is rightly suggesting is you really need 2 different types of press,hydraulic for heavy press operations(crank pins,sleeve gears etc) and a mechanical press for jobs where you need some tactile feel for the job in hand.

Why not consider designing yourself a ratcheting press similar to the design in John's photo?.....OZ.

p.s. John, I really like the look of that ratchet press.

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