Arbor press project

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wildcatter

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Hi guys, I have a project I am working on and am looking for advice . There is a lot of experience here that would be valuable here as I am just a doing this as a hobby so don't have much experience.All the larger presses are crazy expensive so I decided to build one capable of broaching keyways. I have a 1.5 wide rack and a matching gear so now am trying to fab up the head assembly before welding it to the frame. What kind of clearances should I have for the rack to move in? would .005" be too tight? Also, what is the purpose of the brass slider that runs on the smooth side of the ram, for gear tooth clearance or to prevent the ram from dropping down from it's own weight? How much tooth clearance do I need ? Any help or suggestions would be greatly appreciated! I am very impressed with the amount of knowledge and experience shared here . thanks in advance for any and all help.
Dave
 
Well, as a suggestion, the Harbor Freight 29 ton press has been a terrific arbor press for me. I made a bunch of keyways in spacers for my horizontal mill, it worked perfectly. There is far more than 0.005 slop side to side, but in actual use it does not present a problem. I think the slop goes away soon as some pressure begins. I also converted to an air actuated jack and made an assortment of rams, dies and blocks to make positioning quicker…not much need to reposition the lower table.

The large throat height you can get with this press is necessary for many keyways because the broaches can be a foot or more long just in themselves.
 
As to ram clearance is concerned, .005" should be enough, as to gear clearance, you should compute the pitch diameter of the pinion gear and figure what the distance to the backside of the ram should be and arrange the distance from the pinion center to the back face where the ram runs.
The clearance between the bottom of the rack tooth and the OD of the pinion tooth would be about .020" depending on the diametral pitch.
 
thanks for the replies! so just to confirm my calculations, pitch height of the ram is 1.375 and pitch diameter of the gear is 2.5. so I should make the gear center line and the back of the ram 2.63 inches apart . Does that sound right?
 
OK, How did you calculate that? I feel like I'm missing something. ( not an unusual feeling) haha I guess that's why I'm here
 
OOPS . my calculator was set on "accounting" mode. benmychree I am glad you caught that. Thanks!!!
 
Arbor presses have gibs- usually brass plates or brass tipped screws to maintain clearance. A 3/8' broach might appear very stout compared to a 1/16" but the proportions are nearly identical. Like thread taps, they do not absorb side loads. Little of the cutting action occurs when first started in the bushing, .005 in the ram is multiplied by overall length of ram and broach.
That's why a broach is not pushed through in one stroke; back off ram periodically and allow each to reposition. I grease the back of a keyway [and shims] of broach, applying cutting fluid to the teeth.
A bit slower, but never broken a broach, key type or full like a hex.
 
Thanks for the info Toolmaker51. When I mount the gears to the frame my main concern will be keeping the ram perpendicular to the base when welding everything together.
 
Haven't looked at your design; why not fabricate and weld then finish slot for ram after. Shouldn't be hard indicating platen face to 'Y' axis, let 'X' do the rest.
 
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