Alright folks , I got the gear book (gotta brush up on my math !) ... and I got some messed up gears on the lathe that need replacing . My research indicates that the most flexible setup (though not the "best" for every task) is a rotary table with indexing capability . My next decision is size . My baby mill has a max of 18" table to spindle . The table is 9X32" and moves 8X21" . I'm thinking that 6" might be a bit too big , most of the gears are in the
2" to 5" diameter range ... but I don't want to limit myself to what may come in the future . 3" is definitely too small , 4" is iffy , and I haven't seen a 5 .
Wrong answer. You need a proper dividing head and tail stock to match. These come with chucks and are quite stiff. An indexing table has no chuck. If the gears are helical or hypoid the dividing head should be differential as well, but that also require a drive setup from the table leadscrew to a gearcase with changeable gears. By your description of your mill, it will not be capable of this. So all you can make will be straight tooth gears. You did not state whether your mill is a horizontal or vertical, but the mill must be horizontal or a vertical with a special horizontal drive, because the only cutters that I know of that are available for the different tooth patterns and pitch diameters come in 8 cutter sets for horizontal arbors. Steve
It's a vertical tabletop model . I want to make my own cutters on the lathe/mill, and cut straight cut gears to replace some with broken teeth for my Logan Lathe . There will be other tasks which require a rotating table , not necessarily indexed that closely . I'm looking for FLEXIBILITY in addition to CAPABILITY . Most rotary tables also have a MT hole to mount centers , and slots that can mount a chuck if needed . Widen your field of view , Steve , you seem to have a case of tunnel vision .
----------------------------------- Actually this is the answer if you have bags of money and space.
Assuming you don't, and the lathe gears you are talking about are straight cut change gears, the rotary table should work quite well. It just won't be as quite as rigid, and there will be some gear teeth numbers [prime generally] you can't cut because the dividing plates won't have the correct number of holes.
The work around is to use the vernier settings and directly machine the gears, or drill a plate with the correct number of holes. Because of the way dividing heads work, the spacing will be more accurate by the dividing head gear factor. If you are extremely annal retentive you can use this plate to drill a third yet more accurate plate.
While some of the rotary tables /dividing heads have B&S or other tapers, most of the new ones are #2 Morse tapers in the smaller sizes but be sure to check. The one I have is
fits [snuggly] on my Emco Compact 10.
dividing plates are extra
The Little Machine Shop has machinable #2 Morse taper arbors that will greatly simplify your task, as these are pre drilled/tapped for a spindel/retention bolt, and only need the head machined to the correct diameter. If you don't have a #2 taper adapter for your lathe, get one of the sleeves and use a 4 jaw chuck. [Or a MT adapter to fit your spindle but you will most likely have to saw the back half off.] These are also available in #3MT and work well for making the single point fly cutter described in Law's book.
?PMAKA=214-8705&PMPXNO=945794&PARTPG=INLMK32 Depending on the accuracy desired you can hand grind a single point tool to fit an existing gear or buy B&S style involute cutters. As indicated in Law's book these cover a limited range of teeth, but for most shop use you will only #s 2,3,4 [26 to 134 teeth]
[be setting down when checking prices also note that some of these are UK suppliers]
of the few US suppliers I have been able to locate is
Be sure and get an arbor to fit your mill spindle at the same time.
Also order a slitting or slotting saw of the correct thickness w/arbor to hog out most of the material to reduce the load on the hard to grind single point cutter or expensive formed cutter.
(1) unless functionally required, make the gears flat sided with no undercuts. Typically store bought cast/forged gears are dished to reduce the amount of material. This leads directly into hint 2. (2) Cut the bigger gears first. Then when you ding one you can turn it down to a smaller size blank, and not lose the work you did machining the bore, key way and probably the thickness.
Also it may be helpful to install a pin on the gear arbor that will engage the drive slot in the gear bore. This is particularly helpful when lathe turning the OD and thickness of the gear, although you can do this with an end mill and the rotary table.
Also consider alternate materials for your change gears. In many cases the manufacturers used cast iron because that was all they had. Phenolic/Formica, delrin, nylon, and possibly aluminum may be a better alternative, cheaper and more easily located. 6061 T6 has worked well for change gears for my Emco.
?PMAKA=510-1722&PMPXNO=8914298&PARTPG=INLMK32 Good luck and let the group know what you decide and how you make out.
Unka' George [George McDuffee]
------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Greetings Terry, I have a 4, a 10, and a 12 inch rotary table. It seems that no matter what I'm trying to machine it's something bigger than the table will easily handle. So if you can get a 6 inch table that is low enough for your mill that's the one to get. And make sure it's a horizontal/vertical one. When you get your rotary table one thing that's a BIG help is to make a longer handle for turning it. So you will need to tap another hole in the existing handle wheel 180 degrees from the existing hole. Then use a piece of bar stock to extend the radius so that the handle is now at a 3 or 4 inch radius (or so). Drill two holes to match the holes in the wheel and tap a hole to match the handle you unscrewed from the wheel. Even though your hand will now be travelling farther because you will be swinging it through a larger radius the extra leverage makes it much easier to control any movement of the table. And just like the gear reduction makes small errors of indexing even smaller so does the extension handle. Cheers, Eric
Perhaps you are approaching the problem the hard way. First check a place that has stock gears. Often these can be had and then easily modified to fit in most applications and the hard work is all done.
Yes, this is probably the most flexible setup. For my bridgeport, I have an 8" Horizontal/vertical Phase II rotary table with a tailstock and a set of dividing plates, and a homemade adapter to mount a 4-jaw chuck on top. I also found a surplus 4" universal dividing head with a 3-jaw chuck attached (beautiful thing) later on but I wouldn't have bought one as a first choice new.
What you need to do is run the rotary table in vertical mode with the tailstock, with the gear on an arbor in between centers. Depending on the tool, you'll be running either a commercial multi-tooth form tool in a slitting saw arbor, or a single point tool in a flycutter/boring bar holder (which you'll probably have to make yourself). Set the cutter on centerline vertically, set your depth of cut with your y- axis dial, and use your x (longitudinal) feed to cut each tooth. You'll probably need to take more than one pass, going all the way around the gear each time.
Be sure the cutter forces the gear toward the larger end of the arbor. If you use a live center and driving dog remove *all* play from the dog.
You can make the holder from a large bolt. Center-drill both ends, turn the shank to fit a collet, then cut a slot across the head for the bit and add clamping setscrews. A larger, fine-thread tap like
10-32 or 1/4-28 is less likely to break. Try to put the bit's cutting edge radial so it will be easier to shape and regrind. The Grade 5 bolts I've used turned easily to a very good finish.
Center it on the tailstock point, for instance.
You can cut one tooth slot almost to full depth for a short distance to mark the tooth outline, then rough all the teeth out almost to that outline with a Woodruff cutter. You have to feed a one-tooth gear cutter slowly, especially on the finish pass to avoid rotation marks.
I needed a splined shaft to press into a motorcycle sprocket, with 13 teeth which my rotary table can't do, so I took a 52 tooth change gear for the AA lathe, made an indexing stop to fit between the teeth, and put it on the same shaft as the gear blank. I cut the slots slightly undersized and pressed the sprocket on, and the thin chips the sprocket shaved off looked even all around.
If you have a similar gear to copy, make a fixture that fits the gear's center hole and guides the bit radially into a tooth groove. Use it to fit the bit so no light shows between the bit and a tooth. The one I made was an aluminum bar with a hole for the shaft on one end and a 1/4" slot for the HSS bit on the other, milled at the same table Y position to make the slot radial. The bit slides in the slot with minimal side play.
You could soot the bit in a candle flame to find the contact spots you need to grind down. I couldn't get bluing to work well enough on smooth HSS. Mark the center of the bit so you can align it with the tailstock point.
I used the unfinished bit for roughing the slots, alternately taking a pass around the blank and grinding the bit to fit a little better. That way it was always sharp. It was hard to grind both the tooth curve and the back relief properly with a Dremel, so I gave it excessive relief and it dulled quickly.
This description is a mix of two jobs, trapezoidal splines for the motorcycle sprocket and involute splines for a hydraulic gear pump. Both were press fits that carried several horsepower.
That's what I love about this place . Creative minds willing to share their ideas . My appreciation to both of you , both have given me more food for thought . I plan on turning multi-tooth cutters (think shaped rings with teeth cut into them) for the two DP's used on my lathe . The centered cutter cuts to depth with straight sides , the cutters to either side of it shape the flanks of the adjacent teeth . To do this I will need the table vertical , the gear blank on an arbor , supported by a tailstock . I like the idea of using an existing gear as an index , but am concerned about my ability to do it accurately . I will be using an arbor that has a 3/4 shank and a 1" dia with a key slot on the cutter end . I have made a flycutter , 12 deg angle at the bottom (back side of the bit on CL , using AL4 brazed 1/4 by1/4 cutters) that works well , and my first attempt at indexable end mills works , but I believe really needs coolant/lube to work really well .
Think "hob". I never made one because Boston Gear sells gears I could bore out to fix my South Bend lathe. Hint: don't jam a screwdriver into the gear train to lock it if the chuck is too tight. @#$%^ trade- school kids.
A straight hob such as you described can cut perfect gears if you roll the gear across it, the problem is to synchronize them.
I think the easier method uses a spiral tooth hob, like a worm gear, but the blank is tilted so the hob cuts straight across it. The hob turns the blank and automatically cuts the proper involute curve on the teeth as they roll through the cutting edges. Descriptions of hobbing on a horizontal milling machine suggest gearing the hob spindle to the rotary index if possible. Rough the spaces out first.
The gotcha is threading the hob at the correct circular pitch to match the existing gear.
Me too. Before finding the 52 tooth gear the plan was to make a 13 hole ring for the rotary table.
Lube yes, coolant no. I use it if the machine has it but at home just brush on a little cutting or pipe threading oil. Speed is 80 - 100 FPM, less with home-made cutters that could break or fly off.