Rookie Lathe Soft Jaw Questions

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Harold_V
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Re: Rookie Lathe Soft Jaw Questions

Post by Harold_V » Sat Jan 08, 2022 4:11 pm

One may or may not be able to measure the bore of soft jaws. I rarely can, as I do not own intrimiks. That doesn't prevent me from achieving the desired fit. That's quite easy to do, assuming you think beyond the end of your nose. Once near size, the first .03" of depth can be bored until the part enters. Once it does, one backs off on the dial a few thou, until the fit of the part is achieved, then bores to desired depth, and faces the shoulder. By advancing the boring tool in thou increments, an ideal bore size can be achieved.

Sure--this takes time. But how much time would it take to replace parts that are scrapped due to less-than-ideal workmanship? And remember, especially if multiple parts are being machined, any time spent making the ideal setup is repaid by the ability to rapidly load and unload parts, holding them without doing any damage. The depth stop is an added bonus, and assures the parts are held in proper attitude.

H
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rmac
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Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Sat Jan 08, 2022 5:39 pm

This board is great! It's amazing how a simple question can lead to interesting and informative discussions like this one.

I spent a lot of yesterday overthinking the jaw length vs. scroll engagement compromise and trying to decide whether or not to center the soft jaws lengthwise on the master jaws. Of course neither of these questions has a clear answer because, as somebody recently noted,
Harold_V wrote: It goes without saying, one can't predict the size of work that will be demanded tomorrow.
In the end I decided to make the jaws like my original drawing shows, except a little bit longer to so maybe they'll last a little bit longer.

FWIW, as part of yesterday's exercise, I took a good look at my 6-1/4" 3-jaw chuck. The master jaws are about 2-1/4" long, and the scroll engages about a third of that length, or about three teeth. So pete's three-tooth rule is just barely met by this chuck. As you open the chuck from the fully closed position, the jaws begin to disengage from the scroll when they've moved about 1-1/2" and are set to accept a 3" OD part. For parts larger than that, flipping the hard jaws around gives additional range.

Thanks one more time for the lively exchange.

-- Russell Mac

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rmac
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Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Tue Jan 11, 2022 9:54 pm

Soft jaws are done. I decided to make the keys loose instead of part of the jaws as in the original drawing. That made for a little less milling and a little less wasted material.

I made the counterbores deeper than in the original jaws so I can machine away more of the soft jaws before running into the cap screws that hold them to the master jaws. Now I gotta get some shorter cap screws before I can actually do anything further. And make a spider.

To cut the pointed ends, I made a quick and dirty plywood cradle to set the jaws at (close to) the correct angle in the vise. I'm wondering how you'd do that if you needed the angle to be exact.

-- Russell Mac

jaws_installed.png
jaws_posing.png
cradle.png
Last edited by rmac on Wed Jan 12, 2022 12:09 am, edited 1 time in total.

bill jones
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Re: Rookie Lathe Soft Jaw Questions

Post by bill jones » Tue Jan 11, 2022 10:29 pm

---I put the chamfers on both ends---or maybe machine the OD to have precise gripping edges capable to grip larger tubular parts from the inside---and then leave a locating stop at the back end of those grip lengths

---if you put the chamfers on both ends this allows one more inner diameter size if you install those ends inward---so that set of jaws can have the insides bored to suit a different size at either end---and turn'm upside down

---I also engrave a number and a letter designation in the exact same reference area---so when you get about 30 of these soft jaws laying around you can determine which 3 are to a specific set---and which ends belong as the inner end and which are the outer end

---I also made a simple flat rack plate about 4" wide and 4 feet long---attached it to my lathe tilted up about 45 degrees---with some slots for the fastener threads to slip into

---and I have a set of fasteners each with a sturdy thick washer for each set---because after usage those aluminum holes want to deform and close inward onto the fasteners

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rmac
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Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Wed Jan 12, 2022 7:38 am

Thanks for the hints, Bill. I wouldn't have thought about the engraving or the need for washers. I don't have any particular use for these in mind, but I figured someday I might want to flip them around and use the non-chamfered ends for larger diameter workpieces. Hard to predict the future.
Last edited by rmac on Wed Jan 12, 2022 7:40 am, edited 1 time in total.

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GlennW
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Re: Rookie Lathe Soft Jaw Questions

Post by GlennW » Wed Jan 12, 2022 7:39 am

bill jones wrote:
Tue Jan 11, 2022 10:29 pm
---and I have a set of fasteners each with a sturdy thick washer for each set---because after usage those aluminum holes want to deform and close inward onto the fasteners
Sounds like there may be some serious over tightening of the fasteners happening there. The keyways locate the jaws and keep them from moving around, The fasteners just hold them in place.
Glenn

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Re: Rookie Lathe Soft Jaw Questions

Post by RSG » Wed Jan 12, 2022 8:39 am

bill jones wrote:
Tue Jan 11, 2022 10:29 pm
I also engrave a number and a letter designation in the exact same reference area---so when you get about 30 of these soft jaws laying around you can determine which 3 are to a specific set---and which ends belong as the inner end and which are the outer end
Awesome point Bill! One I should have mentioned as I do the exact same. I figure I have about 20 sets as well and keeping track is important.
Vision is not seeing things as they are, but as they will be.

bill jones
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Re: Rookie Lathe Soft Jaw Questions

Post by bill jones » Wed Jan 12, 2022 10:23 am

---here a link back to one of my soft jaw sets
viewtopic.php?f=42&t=110015&p=430729#p430729

Inspector
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Re: Rookie Lathe Soft Jaw Questions

Post by Inspector » Wed Jan 12, 2022 1:56 pm

"Soft jaws are done. I decided to make the keys loose instead of part of the jaws as in the original drawing. That made for a little less milling and a little less wasted material."

What keeps the key from coming out of the jaw during use?

Pete

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rmac
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Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Wed Jan 12, 2022 2:42 pm

Inspector wrote:
Wed Jan 12, 2022 1:56 pm
What keeps the key from coming out of the jaw during use?
With any luck, friction. The keys fit snugly into the jaws to start with. Then as the master jaws exert force on the soft jaws (through the keys) when clamping a part, the keys should be locked in pretty good.

-- Russell Mac

Edit: Back in 2007, SteveM showed jaws he made with loose keys. I think Harold indicated in the same thread that his jaws also use separate keys. Steve and/or Harold, if you're listening, have you ever had trouble with the keys coming out?

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SteveM
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Re: Rookie Lathe Soft Jaw Questions

Post by SteveM » Wed Jan 12, 2022 4:42 pm

Inspector wrote:
Wed Jan 12, 2022 1:56 pm
What keeps the key from coming out of the jaw during use?
If it worried you, you could just take a center punch and make a pip on the side that would grab into the aluminum.

Steve

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Re: Rookie Lathe Soft Jaw Questions

Post by Inspector » Wed Jan 12, 2022 6:30 pm

The centre punch mark would do it but then it dawned on me some Loctite would work too. That makes the soft jaws fabrication method easier and safe too.

Pete

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