Small (broach) press. Hydraulic or mechanical?

[PekkaNF]

I have no good press on my workshop. I have been tempted to buy one of the cheap table top shop press thingys, but they are too small and too big at the same time.

I need something small, lightweight, easy to dismantle and store solution. I generally don't need very much grunt or use big parts though.

People have tendency to do a lot of compromises, but I'm having a lot of problem with universal tools that do nothing well.

My most immediate need is to broach some 6 mm and smaller keyseats and there is one inspiration:
http://images.wdsltd.co.uk/7400/11/marlco-heavy-duty-two-speed-broaching-hand-presses-wds-6551

There is one of right size, but this is for pull broach:
http://modelengineeringwebsite.com/Broach.html

I need about 350 mm of continuos stroke. I don't like to put any packing pieces and such to extend stroke.

I think I need about "1-2t" of force. 6 mm broach is quoted of 1000 kg and 8mm for 1700 kg.

I don't want it big I'm thinkking of max 150 mm dia parts between on two colums. Bigger ones must be boltted on the base or something.

1) Hydraulic, I have one hydraulic auto frame puller kit. I has a hand pump and 4t push cylinder with 125 mm stroke.

I have palans of using this as a small bearing press, haven't "found" small C-frame for it, probably need to fabricate one. At first it sounds good, but continuous stroke lengt is not enough. Therefore I would need another hydraulic cylinder and brocah movement would be pulsating because of the hand pump.

Is non continuos movement a problem for broaching and bearing assembly?

2) Arbort press. I found almost two meters long round bar that has module 1,5 tooth rack on it. Both ends are knackered and 100 mm of the rack is crap at the other end, but most of it looks usefull.

I did some fast calculation and it looks like this tooth module is way too small to transmit more than 400N of linear force. Way too litle. Am I off by factor of 1000 or something? Commecial arbor presses seem to use whole lot more coarse module.

That would also need a rachet mechanism or mighty big wheel. If I can't use this rack I sould buy all parts and then I'm not that thrilled.

Although it looks like this approach would produce small footprint and small storage space press.

3) Screw jack. Starts to look like best canditate. Trapezoidal threaded bar and nuts are not that expensive.

Push screw arragement looks simple and compact, but probably would need a pretty big diameter screw to keep it from buckling. Pull screw would probably be cheapest but lenght would grow and I would like to keep underside of the press unocupied from he junk. This would allow ocassional broaching of the bigger parts.

And I have two 0,55/0,75 KW worrm gear motors that has output speed of 100 and 140 rpm.

Very tempted to buy 1 metre trapezoudal thread bar, cut it half, couple two nuts together, but thread bar on pull arragemet and power them with a gear motor. 4-5 mm advance would give pretty decent speed and probably even enough force.

These gear motors have hollow secondary ID 25 mm with 8 mm key seat and gear has a reaction bar. This should make it pretty easy to mount and disassembe it between uses. I have another workshop application in mind and planning to switch motors between units.

Unfotunately gear motor bearings can't take axial force and secondary shaft hole is only 25 mm. That is a bit too small to use trough the gear thread bar and couple the nut into it. Would make it very simple.

I don't have any good experience on key seat broaching (other than I'm not going broach 6 or 8 mm key seat on lathe).

Which one of those approach would work best on push broach and why? I need to build the frame and bits anyways. I'm plannig of buying the push broaches, but I'm making the shimms and bushings as I need.

Pekka

[Lew_Merrick_PE]

Hi Pekka,

So, you want to broach keyseats for ø6 and ø10 mm bores.  Correct?  (1) How thick are they going to be?  (2) And how long until you need to keyseat a (say) ø20 mm bore?

A (male) screwthread does not make all that stiff a column (though a proper choice can be made).  You are better off building your stiffness into a "column guide."  That way the screwthread is only providing the "push."  As I am in the U.S., knowing what sizes of CRS (Cold Rolled Steel) bar are available to you is not something I would know.

Basically, if you need 350 mm of "throw," you are going to need something like 475-500 mm of "column" to allow a "reaction carriage" to carry the bending load.  (That being an off the cuff statement rather than one backed up by calculations.)  My basis for this statement is that, a few years ago, I developed a "drop test fixture" for use in a vacuum chamber where the piece being "dropped" was (about) 4.5 tonne.  I was able to support it (and meet the NASA fixture requirements) using three ø1.000 inch CRS bars that were 40 inches (a bit more than 1 m) long and still have a margin of safety to yield greater than 3.

Another approach might be to look into the hydraulic cylinder from a mechanic's engine hoist.  That is the beast I use as my shop crane to move heavy (2 tonne) objects.  The cylinder itself has approximate 6 tonnes of capacity and a 30 inch (760 mm) stroke.  Such engine hoists can be had here in the U.S. for about $250 new and $75 used the last time I looked.

I have avoided getting into the strengths of metric screwthreads because of the five variations in allowance and tolerances currently allowed by the various standards.  In the U.S. "ISO" version, a heat treated M16 X 2 thread should carry 152 kN of load without yielding and an M15 X 1.75 heat treated thread is rated at 82 kN.  (Your "milage" will vary!)  This "suggests" to me that a screwthread approach is likely to be less expensive.

Does this help?

[PekkaNF]

yes, that helps

I will be mainly making keyseats to 18-30 mm ID holes. Key width will be 6 or 8 mm. Mostly 6 mm keys to 20 and 25 mm bosses.

I was thinking of using long bolts or allthread (two common different grades to choose) for upprights, but it does not looks like best of the ideas. Anything will do. Now I'm thinkking of using 20 or 35 mm cold rolled steel

Right now I'm trying to find out is it:
a) Use steady and continuous feed as with trapezoidal thread and gear motor or hydraulic pump?
b) Or is discontinuous feed more or less ok? Yankking with a hand pump (hydraulic ram). Rachet feed with a gear rack or screw?

Reason is that I had a chat with one gear designer and he was pretty insistent on continuous feed.

Pekka

[Lew_Merrick_PE]

The advantage of a continuous feed is that the cut itself will be smoother and the chip form will not attempt to re-weld itself to the seat.

[RodW]

If it helps, I cut a 4mm keyway in a 12mm bore using a commercial Dumont Minute Man broach the other day with this 6 tonne  benchtop press.




I have drilled an extra hole to gain maximum throat depth in the press and also made up a shorter press shaft to gain the clearance I needed to do the job shown. I had to reposition the part to complete the operation.

I have heard that you can shatter a broach with a hydraulic press so I was very careful. The press is not very accurately built.

Some guys have built broaching tools for their lathe and move the cross slide to take thin cuts in multiple passes.

I bought this little press to do the job shown and pull it out of the corner every now and again to do something.

[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.

                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.

[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!

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.

[PekkaNF]

Thank you. That starts to make sense. Looks like my tools multiply faster than the space I have.

My first instinct was on arbour press, but soon I realized that none of the stuff i have fits to it. It's all from the drawing board up. The chinese stuff they sell here is really a nonstartter. Way too limitted daylight, not a single part is staright, too little stroke etc. Therefore I should start from the scratch and it looks like a gear module has to go up few notches than I'm used to to take the load. Having an electrical engineering background instead of mechanical engineering I'm having a slight problem on gear rack/pinion module size. Looks like this approach would be fairly expensive or the stuff is dimensioned or manufactured to different standards than off the self stuff I can buy.

I wish there were cheap pull broaches.

But it looks like I have some more homework to do before rushing buying and welding stuff.

Pekka

[John Stevenson]

I'll have a look to see if I have any old photo's of the press with both types fitted but I don't think I will be lucky.
Basically it was a normal hydraulic press like many people build but had a rack to one side of the cylinder with the pinion behind it so you were pulling towards you. The operation was a simple capstan with 4 holes in it and you just kept moving the lever from hole to hole.
A ratchet would have been better but it sufficed at the time.

[PekkaNF]

I got one small and cheap hydraulic unit minus motor and valves. It was cheap and unused.

It has 1,1 cm3/r capacity, 230 bars or so and can take up to 4000 (or 6000 rpm). Needs a motor and came with frame 71 mounts/couplings i.e. 0,37-0,55 kW induction motor parts.

It has cetop3 drilling and some ports I might connect hydraulic hoses right into. It has a pressure relief valve and 10l tank.

I need to see if I could use it.

Pekka

[PekkaNF]

I bought a broach set last night. Waitting it to arrive from UK.

Someone suggested motor hois and incidently my brother noticed one spare motor hoist pump/cylinder unit as a spare. It was 45 EUR, but since it is single action is no go for me when I'm this deep on the other end of the mud puddle. however if someone else is considering DIY that might be a easy way on manual system. Stroke and force looks good enough, it is all integrated much like a bottle jack, just a longer stroke.

Pekka

[tom osselton]

I have bought a 1/4" square broach that I'm hoping the 3 ton arbour press will handle.

[PekkaNF]

I have been doodling some stuff and basic layout is coming out on these lines:

Standard 25/40/400 mm double acting hydraulic cylinder, bought without any mounts/clevises

1) Rod end: Straight (to be pinned) or boss/thread or internal M12 thread

2) Split clamping at front end, cylinder "plain" without any provisions.

3) No clevis or mount on cylinder body.


part (9) is a slide that hopefully prevents the cylinder from bucling. It runs on plastic bushes (8) on drawn steel rods (7). Looks like 25 mm dia is plenty, even with threaded ends.

Pekka

[John Stevenson]

Split clamp is not going to work.
For every force there is an opposite so if you are pressing 10 tonnes then 10 tonnes is trying to push your cylinder out of the clamp.

[PekkaNF]

Jep, it's going to be 2-3 tones and there will we a little feature (I don't have a foggiest idea how it is called....sort of part of a flange) that will take the force. Clamp will just keep it there. I was thinkking a thread but realized that my steady is not big enough for it and and it won't fit trough the spindle.

Pekka

[PekkaNF]

Got home key broach set I bough. Gives something concrete for this project. I see that under 5 mm key size I would not have this sort of problem.

Cylinder guy gave me a quote of 190 EUR + VAT:
* Standard cylinder piston and cylinder end cap as well as cylinder head.
* Any length of standard rod and any shoulder/thread I want on in.
* He would fabricate, weld and machine mount and make custom length cylinder tube.

Standard 40/25-400 mm cylinder is 125 EUR + VAT, I can get is as a "kit" or assembled without the welded mounting hardware. This is tempting but I haven't come up with good means of mounting it.

My initial idea was to make a boss between cylinder tube and cylinder head. My friend calculated that 5 mm thick piece would do, but it needs more depth just outside of the tube to keep it rigid. MFG guy did not like, I should machine that "thickness" of the cylinder head to make the O-rings work between the cylinder tube and head.

Plan B: use all thread as a tie bars and put the whole cylinder on compression. See doodle.

Pekka

[John Stevenson]

Plan B looks good.