Gallery, Projects and General > The Design Shop
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 :wave:
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.
Navigation
[0] Message Index
[#] Next page
Go to full version