Shoptask owners?

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Torch
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Re: Shoptask owners?

Post by Torch »

That sounds like a very doable approach, using the machine VelocityDuck already has. Just needs some sort of shop or arbor press to drive the keyway broach.

One note: the second, 90°, keyway would be much shallower. Like 1/8" vs about 3/8" for the broach guide slot.
toddalin
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Re: Shoptask owners?

Post by toddalin »

Poreba would appear to be the closest spline shaft arrangement, and it appropriate size, easiest to broach. They are still in business.

https://i.ebayimg.com/images/g/4vkAAOSw ... -l1600.jpg
VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

Just so I understand the approach being suggested.

Purchase an off the shelf 27 tooth gear with the correct ID. Then create the keyways?

Could the keyways be done with a file? I know as much about broaching as I do cutting gear teeth.
Torch
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Re: Shoptask owners?

Post by Torch »

Yes, that's exactly right.

Broaching is not particularly difficult. A push broach is a piece of HSS with a row of teeth. Each tooth is slightly deeper than the preceding tooth, so as you push the broach through, the teeth gradually shave the keyway deeper and deeper.

Now, you don't push the broach through by hand of course. You use an arbour press or a shop press or similar. And lots of oil. And cutting fluid. The broach is guided by a bushing, which is just a round slug the same diameter as the ID of the hole you are broaching, with a groove milled lengthwise for the broach to ride in. So, to put it all together, the bushing goes in the hole, the broach is oiled up and started in the slot, and then pushed all the way through with a press. (Broaches are hard and therefore brittle, so don't think you can tap them through with a hammer!)

The most common push broach length is 6". That does not have enough teeth to cut the full depth, so the broach will come with one or more L shaped shims. First pass of the broach is with no shims. Next pass is over a shim. Some sizes may require a third pass over two shims. Single pass broaches are available, but they are much longer, requiring a bigger press and way more expensive.

There are broach kits available that come with two or three broaches in different widths and a selection of bushings in common shaft diameters appropriate for the broach widths. I have a couple, and they are a useful starting point. But broaches are also available individually and you can easily make your own bushings. I am right now in the middle of a repair that has a 20mm shaft featuring 3/16" wide woodruff key. I am making a new pulley hub to fit that bastardized metric/inch hybrid. AFAIK, you can't buy a bushing to make that keyway, but it is a simple matter to make a 20mm bushing with the appropriate size and depth slot to suit my 3/16" broach.

You would do the same. Get a gear, bore the centre out to the correct minor diameter. Make a bushing of that diameter on your lathe. Mill a slot lengthwise down the bushing to guide the broach. Mill a shallower keyway 90° from the first slot lengthwise to be used for indexing your bushing when making the subsequent keyways in the gear. If you get the first slot precisely centred, the edges of that slot against the moving jaw of the vise should index it pretty darn close to 90° while keeping it centred to the endmill. Or make the bushing long, use your spin indexer, and cut off the un-slotted waste that was held in the indexer after the slots are both cut.
Torch
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Re: Shoptask owners?

Post by Torch »

Ok, this time with pictures:

Here is the bushing under construction. Note it has a mushroom head so it won't push through with the broach. Make the slot a few thou wider than the broach so it's a nice sliding fit:
Image

And here is the broach with it's shim. Most shims seem to be 0.30" but verify and use the one that came with the broach:
Image

The depth of the guide slot should be the same as the thickness of the lead in to the first tooth. Remember, broaches are tapered! Don't cut the guide slot to match the thick end or you will need extra shims! On the other hand, if you don't cut the guide slot deep enough, you won't get the broach into the hole you are broaching, so if in doubt, go a hair too deep instead of too shallow. You can always make a custom shim from some shim stock. One of my early home made bushings has a 10 thou custom shim for just that reason ;-(

Don't forget to oil up the bushing and broach. I like to use way oil, but 80w90 gear lube is good too.
Image

Use an arbor press or shop press to push it through. I have a 1 ton arbor press. I wish I bought a 2 or 3 ton press -- not because the 1 ton won't push a broach (it will) but because the bigger ones have bigger throats. The 1 ton is too small to fit most parts with the broach. I use my shop press to start, but finish the last bit with the arbor press if I run out of piston on the shop press. Note the long toothless shank at the top of the broach. That determines the thickness of the piece that can be broached. The uppermost tooth must clear the bottom of the keyway before the press hits the bushing.
Image

See the little curlique between the teeth? Those are the shavings from that tooth. MAKE SURE YOU CLEAN THEM OUT BEFORE TAKING ANOTHER PASS. Failure to do so will result in too many curliques in too little space. The broach will jam. You will apply more force. You will break the brittle broach. Don't Ask Me How I Know This (TM).

Speaking of things that break broaches, I like to back off the pressure briefly every few teeth, just to make sure nothing is being forced sideways. Sideways is another Bad Thing.
Image

After the first pass, insert the shim between broach and the back of the guide slot. Oil it up an do it again! Make sure the leading end of the broach is engaged in the partially cut keyway first though, or you will end up with a really sloppy keyway. Again: Don't Ask Me How I Know That (TM).
Image

Ok, with a little bit of luck, this is what you end up with; nice square sharp corners at the correct depth:
Image

Of course, the proof of the pudding is in the eating:
Image
toddalin
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Re: Shoptask owners?

Post by toddalin »

Just so you guys know, this is what he is dealing with. If the broach cuts "perfect angles" that may not quite line up with the spindle, which is "sloppy" toward the base circle, though it would probably work with a bit of filing.

Image
toddalin
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Re: Shoptask owners?

Post by toddalin »

An update:

When my machine broke the spline shaft for the threading gears, it was not Grizzly I got a replacement from, but rather Smithy.

Go toward the bottom of the page and look at the Pulley Box, Diagram #14, Part #C30143, Gear 27 Tooth.

Could this be what you need? And if it is not, could they have it, if not for this machine, than maybe one of their others?

Like I said, I got my shafts from them (shown in my picture) that fit the existing threading gears and only had to cut down the length on the mill.

https://cdn.shopify.com/s/files/1/1845/ ... 1606850051

Alternatively, go to Lathe Head, Diagram #5, Part #30118, Spline Housing. I do believe that that is the spline shaft that I ordered and fits the gears and shown in my picture. If you contact Smithy, you could reference this part that the gear must fit over so they know what you are talking about.

Part #7, C37001 is the fitting gear, but the number of teeth is not listed. (Part #6 lists 50 teeth and is much larger.)

Also, you now know to ask if Part# C30143 (27 tooth gear) will fit over Part #30118 (spline housing) and if so..., that should do it..., assuming they have any of this stuff anymore.
VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

This looks promising!

Can you tell me what the ID of the gear and keyway is (Or the OD of the spline and hub)?

My 27 tooth gear is .597" (15.17mm) ID and .709" (18mm) at the keyway. The ID looks like it might be close to yours.

And Smithy only wants $10 for the 27 tooth gear. :D
toddalin
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Re: Shoptask owners?

Post by toddalin »

Like I said, I bought three replacement spline shafts from Smithy and they all differ by just a hair

Smithy spline shaft (extras):
across round portion: #1-0.578", #2-0.578" (very tight fit on my gears, but they do go with minor coaxing), ShopTask original (broken in length, cracked in diameter), 0.563" (easy fit)
across splines: #1-0.705", #2-0.707", Shoptask original-0.706"

BTW, the one I ended up using (not measured) was a hair smaller for the round portion because my gears went right on it whereas they are very tight on the other two (which is exactly why I bought three).
VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

Thanks!

Shipping was more than one gear so I ordered two. LOL
Torch
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Re: Shoptask owners?

Post by Torch »

Oh well that just takes all the fun out of it. <lol>

Congratulations. Go make some chips. ;-)
VelocityDuck
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Joined: Mon Dec 07, 2020 6:14 am
Location: Panama City, FL

Re: Shoptask owners?

Post by VelocityDuck »

Just to close out this part of the discussion.

The gear from Smithy works... After a little fine tuning with some needle files. It just didn't want to slip over the arbor. But after about 30 minutes, she's working fine.

Now threading with this machine is just plain weird. I understand this machine is different, but damn! :lol:
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