How Do You Space Teeth On A Rack

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Reeltor

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Can anyone confirm, or tell me how to space the teeth when machining a rack (as in a rack for a rack and pinion gear)?

I need to cut a rack and matching gear in 4DP

In the free Google Book download of Cincinnati’s A Treatise on Milling and Milling Machines page 262 says to space the first tooth turn the crank 3 times plus 35 thousandths. Not having a Cincinnati mill, I am not sure how much a full turn of the hand-wheel will move the table. Is it 100 thousandths per full turn? Making the spacing 3 hundred and thirty-five thousandths?


The project is to make a “kinetic” log splitter. My daughter purchased a DR Rapidfire Split log splitter http://www.drpower.com/power-equipment/log-splitters/rapidfire-splitter/prompt-for-rapidfire-3-hp-ms-new---web.axd , It looks like a pretty simple design that can be duplicated for a lot less than $1,300.

A quick YouTube search turned up this excellent up-scaled version

The maker provided the Martin Gear part numbers for his splitter. The pinion gear is Martin Gear’s #S415 a 4dp, 4-1/2” OD 15 tooth, with a 2” face. ($166 on Amazon) and Martin Gear’s R4x4 rack 2” x 2” is $447. At those prices you might as well as buy a complete DR Rapidfire.


I picked up the material for the rack last spring, and just scored a complete 4dp gear cutting set of 8 on ebay. A visit to Metals Supermarket and found a 6” round of 8620 for the gear. So far I’ve got $49 in materials, plus $120 for the set of gear cutters. I still need a 4” by 6’ H-beam, some scrap plate to hold it all together and a cheap HF engine to run it.


Mike
 

Attachments

  • Table for Cutting Racks, page 262 Treatise on Milling.pdf
    2.8 MB · Views: 13
This link to Boston Gear spells out most of the terms in gear cutting. https://www.bostongear.com/pdf/gear_theory.pdf
For your 4DP rack the spacing is .7854 inches.
Curious what type of mill you have, if a horizontal you can only cut teeth to the length of the arbour, on a vertical you need a right angle drive.
I've cut racks on the shaper for those reasons.
Greg
 
another thing to remember is to use stress relieved material otherwise you will end up with an arched rack when released.
 
Another consideration yet is that a kinetic splitter probably puts a huge load on those teeth. 4DP is a big rack, but I wonder if the rack and gear need to be hardened and tempered to take the stress and strain?
 
nice fun project BUT may be store bought is the way to go, when you consider the cost of materials.
 
Thanks for the responses; please keep them coming :)
Ed, With materials that I have on-hand I think I can come in at under $400 for the build. The biggest hindrance was the gear cutters. I didn't want to grind my own bit and use a fly cutter to cut the gear. Now that I have a set; I can match the number of teeth to the 6" round of steel that I picked up.
Bob, I do plan on hardening the pinion gear and use a (soft) key to protect the gear teeth. The RapidFire has the pinion teeth cut directly into the axle holding the flywheel(s). I they are induction hardened (I think) only at the gear teeth. I am up in the air on hardening the rack
BillH-- I have a hot-rolled bar for the rack, hot-rolled should already be stress releaved, I don't expect it to banana
Greg, I have a VanNorman 22L that can be setup to run both horizontal or vertical. Planning on keeping the mill in the horizontal mode; I'll cut the gear first using my dividing head. The Martin Gear that the YouTube user used has 15 teeth and is 4-1/2" in diameter. I am going to look into the advantage of increasing the number of teeth since I have 6" to work with.
I do have a 16" shaper but haven't gotten it up and running, at this point I don't know if I'll cut the rack on the mill or try to get the shaper running.
As for the spacing, I'm not 100% positive how/where the .7854 is measured from. The chart in the Cinci book seems to say, cut a tooth, move .335 and cut the next one, repeat.

thanks again, Mike
 
That chart in the Cincinnati book doesn't make sense to me, can't figure what a full turn would be. The spacing is measured at the pitch dia, (about half the depth of the tooth)
The pitch diameter is the number of teeth in a spur gear divided by the Diametrical Pitch. Say for a 10 tooth gear, PD=10/4 or 2.5 dia. Circumference is PD * PI = 7.8534. Divide by 10 teeth and you get 0.7853. When you get to a rack the diameter is infinite.
Hope that makes sense. Took me a while. If you use the shaper the cutter is straight sided ground to match the pressure angle of your spur gear.

Greg
 
Thank you for the responses on how to set the teeth on the rack. I am now working on the gear that will mesh with the rack. Once I finish the gear it will be on to the rack.
 
After you do all your math, roll the oiled gear through some modeling clay thats been flattened out to double check.

Sent from somewhere in East Texas Jake Parker
 
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