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EddyCurr
02-26-2017, 03:48 PM
A 6" Burnerd 4-Jaw Independent Iron Body Chuck - Series 34 has one operating screw that is cracked.

The cracks are visible at two of four corners of the broached square wrench socket. They extend from the lip of the mouth down to a depth of one thread. Either it was a simple matter of too much torque applied or maybe the chuck wrench was not fully inserted. Perhaps someone tried to remove the chuck by smacking the wrench.

http://www.slalom4me.com/imaged_a01/jpg/other/tools/lathes/SouthBend/2017.02.25_BurnerdChkOpScrew_01.jpg

The screw turns easily in the chuck and I have been using the chuck as is since it arrived here, taking care to tighten the other screws against this cracked one. While cleaning today, I wondered about repair.

The operating screws on this chuck appear to be staked in place - I have not studied this closely, but I will assume that the stake can be removed. Replacement of the screw seems to be hampered by a lack of a ready source for another one. A repair of the hardened and ground screw seems limited to shrinking a collar over the lip at the mouth and I do not think this would gain much.

Any other ideas?

Paul Alciatore
02-26-2017, 04:32 PM
One of my four jaw chucks has screws that look similar to the one shown. There is a key that is inserted in a slot from the rear and that rides in the groove in the center of the threads on the screw. That key is what holds the screw in place.

Those keys are made from flat, ground steel and have a half round cut in one edge to fit around the groove in the screw. They are a tight fit in the slots in the body of the chuck and are held in place by some set screws that are in holes that were tapped across the boundary between the key and the chuck body. You just remove those set screws and then work the key out - I did say it was a tight fit. Then the screw comes out easily.

Your Burnerd probably has something similar. A photo of the back side of the chuck, with the mounting plate removed, will probably show the details.

As for repairing it, perhaps it could be brazed with a steel ring around the neck for reinforcement. Or you could try to purchase an OEM part. I would save making one as a last resort.

You may also want to braze a reinforcement ring on the other three.

EddyCurr
02-26-2017, 05:34 PM
One of my four jaw chucks has screws that look similar to the one shown. There is a key that is inserted in a slot from the rear

... a tight fit in the slots in the body of the chuck and are held in place by some set screws that are in holes that were tapped across the boundary between the key and the chuck body. You just remove those set screws and then work the key out ...

Your Burnerd probably has something similar. A photo of the back side ...The Burnerd looks a little different. There appear to be pressed-in-place slugs.

Underneath these slugs within the body of the chuck, a U-shaped yoke engages 180 of a necked-down section of the operating screw. I do not know whether the yoke is a separate component or machined on the inner end of the slug, I expect the former.

Although the appearance mumurs "No user-serviceable parts within", drilling/tapping might enable the slug to be extracted - if indeed a pressed fit.

http://www.slalom4me.com/imaged_a01/jpg/other/tools/lathes/SouthBend/2017.02.25_BurnerdChkOpScrew_02.jpg

http://www.slalom4me.com/imaged_a01/jpg/other/tools/lathes/SouthBend/2017.02.25_BurnerdChkOpScrew_03.jpg

ammcoman2
02-26-2017, 06:54 PM
I have an 8" PB 4 jaw that has one cracked screw when purchased, but it has hex sockets. I just live with it as the crack is shallow. The ones in your chuck appear to be deeper.

Perhaps Rotagrip in the UK has a replacement like this one:http://www.rotagriponline.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=4854&category_id=39&option=com_virtuemart&Itemid=29
They also have square thread ones for 6" chucks.

A few years ago I got a set of soft jaws from them for a PB 6", 3 jaw. They did fit after a bit of scraping - then machined them into outside jaws.

Another solution is to make one - a morning's task!

Geoff

BCRider
02-26-2017, 08:13 PM
The collar at the end is usually very close in size to the minor diameter of the thread. So I don't think a collar of any usable thickness is a realistic option.

I'd be leaning towards TIG welding the cracks at the collar and down onto the last thread. And if possible from the inside a short ways into the square recess as well. Done with a light touch and not much time on the joint and a cool down between welding the cracks should provide enough of a repair that thoughtful tightening of the jaw should be possible for years to come.

In terms of affecting the heat treatment of the screw with care and a fairly rapid on then off for each crack the softening from over heating of the metal should be able to be limited to just the weld and the last thread.

RichR
02-26-2017, 08:48 PM
A 6" Burnerd 4-Jaw Independent Iron Body Chuck - Series 34 has one operating screw that is cracked.

The cracks are visible at two of four corners of the broached square wrench socket. They extend from the lip of the mouth down to a depth of one thread.

I see the two cracks you mention at 4 and 7 o'clock. It looks like there is another crack starting to form at 2 o'clock.

_Paul_
02-26-2017, 09:28 PM
I have a couple of Burnerd 4 jaws like yours which have no locating screw holding the retainer, in my experience they are a slight interference fit, looking from the front you will see a small shoulder sticking up either side of the operating screw using a suitable punch a few alternating taps on these shoulders should see the retainer out.
I have never seen one drilled out.

Paul

digr
02-26-2017, 10:02 PM
I have knocked those retainers out from the front with a forked punch.

mattthemuppet
02-26-2017, 10:07 PM
same as Paul ^. Once you remove the jaw, you should see a bit of metal on either side of the groove in the screw. These are 2 "prongs" which are part of the plug on the back of the chuck. You can either do as Paul and I did and gently tap the plug out with a punch or drift or you can make a special prong like tool to press on both sides at the same time. Mark the plug and the hole if you're doing more than one. I took my 4 jaw Buck chuck apart to clean out what looked like decades of plastic powder, it was very straightforward.

Personally, for the effort involved in fixing that one, I'd just make a new one. PStechpaul did a nice job on his on here, seemed pretty routine as long as you can grind an Acme (square?) thread cutting tool. Don't know if the threads are LH or RH, which might affect your ability to make a new one. Some nice 4140ph and you're good :)

Daveb
02-27-2017, 07:28 AM
Pratt Burnerd chucks over 4" generally have a circular plug with a forked end for each jaw, it's a light press fit and can easily be driven out from the front, the forks are not hard so use a brass drift. Jaw screws for Imperial chucks are no longer available from the makers. There are at least 2 different sizes of screws for 6" chucks, maybe also for others, check size carefully if buying used or NOS replacements. Dave

MattiJ
02-27-2017, 08:41 AM
The collar at the end is usually very close in size to the minor diameter of the thread. So I don't think a collar of any usable thickness is a realistic option.

I'd be leaning towards TIG welding the cracks at the collar and down onto the last thread. And if possible from the inside a short ways into the square recess as well. Done with a light touch and not much time on the joint and a cool down between welding the cracks should provide enough of a repair that thoughtful tightening of the jaw should be possible for years to come.

In terms of affecting the heat treatment of the screw with care and a fairly rapid on then off for each crack the softening from over heating of the metal should be able to be limited to just the weld and the last thread.

Assuming that this is hardened high carbon/alloy steel part I would be more worried of getting glass hard welds than softening the screw. If going the TIG welding route preheat to 200-300 celsius weld after that.
Small tacks and short TIG welds on hardening steel like 1045 without preheat barely hold together the parts in slightest breeze, the weld has strenght of dry cookie.

Seastar
02-27-2017, 08:59 AM
I had a similar problem in a 4 jaw. I tapped down the keepers a little from the front and braised the cracks.
It's worked for the last 3 years just fine although I don't use it a lot and am careful when I tighten.
I painted that screw red to remind myself.
Bill

Doozer
02-27-2017, 09:44 AM
Leave the cracks alone.
Shrink a sleeve over the spigot
to contain the hoop stress
and it will keep the cracks tight.
No need to even take the screw out.

--Doozer

BCRider
02-27-2017, 10:24 AM
Assuming that this is hardened high carbon/alloy steel part I would be more worried of getting glass hard welds than softening the screw. If going the TIG welding route preheat to 200-300 celsius weld after that.
Small tacks and short TIG welds on hardening steel like 1045 without preheat barely hold together the parts in slightest breeze, the weld has strenght of dry cookie.

You're right. I ran into that one time. Welds were cracking open as fast as I could run a bead. I "fixed" it with a good pre-heat and re-running the welds. It stayed together and didn't fail from some flex testing so it came out all right. But it wasn't pretty. So I read you loud and clear on the idea of pre-heating a part of this sort.

sarge41
02-27-2017, 10:49 AM
Leave the cracks alone.
Shrink a sleeve over the spigot
to contain the hoop stress
and it will keep the cracks tight.
No need to even take the screw out.

--Doozer

Yep, Doozer ( and others) got it right. I would shrink a collar of 4140 on the cracked screw AND the rest of them for good measure. Good luck.

Sarge

Boats69
02-27-2017, 01:53 PM
I had a similar problem on a low cost chuck, decided to use it as learning opportunity. I am satisfied with the result and it is holding up well. The thread however was square and not ACME. I used EN19T, I think similar to 4140. I had to make a rotary broach to get the square for the key done.


Made this:
http://i1313.photobucket.com/albums/t554/boats5/918680B4-843A-4E5D-AA46-AA77EA366E3D_zpszidpkrh8.jpg (http://s1313.photobucket.com/user/boats5/media/918680B4-843A-4E5D-AA46-AA77EA366E3D_zpszidpkrh8.jpg.html)
To make this:
http://i1313.photobucket.com/albums/t554/boats5/6B990BEA-0B78-4B3D-AABC-D6187FC28BCB_zpsv4kt7w9w.jpg (http://s1313.photobucket.com/user/boats5/media/6B990BEA-0B78-4B3D-AABC-D6187FC28BCB_zpsv4kt7w9w.jpg.html)
To fix this:
http://i1313.photobucket.com/albums/t554/boats5/2616AAE3-CDDE-4B08-8DA9-F431BBAC6B60_zpsldfzt3qt.jpg (http://s1313.photobucket.com/user/boats5/media/2616AAE3-CDDE-4B08-8DA9-F431BBAC6B60_zpsldfzt3qt.jpg.html)

BCRider
02-27-2017, 03:08 PM
Boats' second picture showing the cracked away piece is a good illustration of why a sleeve won't work. Notice how the crown of the square recess area is at the same size as the minor diameter of the threading. So there's no room for a sleeve.

Making a new one or possibly TIG welding and repairing the thread is pretty much the only two possible fixes I can see working out.

For a one off such as this I'd mill the square with a small diameter end mill then clean up the corners either with a broaching cutter in the lathe or mill or using a specially ground cold chisel. Small bites of a couple of thou at a time are not hard to shave away at all. I had to do a hex recess in this same way and it went surprisingly easily.

A.K. Boomer
02-27-2017, 05:43 PM
Either it was a simple matter of too much torque applied or maybe the chuck wrench was not fully inserted. Perhaps someone tried to remove the chuck by smacking the wrench.



or --- someone pulled the old classic fire up the lathe with the key in the chuck and it did not have enough clearance for the lathe bed and "wackaroonie"....

BCRider
02-27-2017, 07:26 PM
Those bolts are DARN tough. I'm thinking there's something to the "wackaroonie" theory...... Especially since TWO corners are cracked.

wombat2go
02-27-2017, 09:42 PM
The Skinner 4006 ( 4 jaw 6 inch) for South Bend. this chuck was delivered in 1939 and shows a more rounded corner key square than Eddy's.
https://app.box.com/s/0co5to5aerf4v1xisc8adflz613pb8cg
https://app.box.com/s/kyd5v5nekcp8yonlhde97b5jh8wjpgvu

I change chucks quite frequently.
I brush the spindle nose threads and faces with an old toothbrush at each change.

Initially this chuck was difficult to loosen compared to the 3 jaw, but it is free now.
I use a small rubber mallet with a soft wood block , on jaw 1 as shown.
https://app.box.com/s/uk3ri77xe1iemw15jwlqncizk3frfcad
The spindle chuck loosening impact is taken by the key to the hole in the body.

Robin R
02-28-2017, 12:11 AM
I have 2 Burnerd 10" 4 jaw chucks with hex sockets on the screws, both of them have all the sockets broken in similar fashion, it does make me wonder how Burnerd got such a good reputation.

EddyCurr
02-28-2017, 01:41 PM
Perhaps Rotagrip in the UK has a replacement ...Ahh, thank you. I had heard of Rotagrip with regard to replacement jaws, but was unaware of how extensive a selection of spares they offered. The correct operating screw for my chuck appears to be their #2540-14365 For Pratt Burnerd 5/6in Light Type Chucks 8 TPI (ACME) (http://www.rotagriponline.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=4851&category_id=39&option=com_virtuemart&Itemid=29).


It looks like there is another crack starting to form at 2 o'clock.I hadn't noticed that - thank you.


in my experience [the slugs/bearings] are a slight interference fit. Looking from the front you will see a small shoulder sticking up either side of the operating screw. Using a suitable punch, a few alternating taps on these shoulders should see the retainer out._Paul_, digr, mattthemuppet, Daveb and anyone else I missed; thank you for your advice about removal. Rotagrip calls these parts bearings and their illustration shows the yoke machined onto the end of the slug (http://www.rotagriponline.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=5116&category_id=40&option=com_virtuemart&Itemid=29).

The solution for me is to order a replacement operating screw. Looks like about C$ 50, plus shipping.

As mentioned, attempts to weld hardened material is bound to be fraught. It hadn't occured to me that a ring would foul the threads, but BCRider is correct.

Cutting a new pc w/ 8 TPI ACME threads is no big deal. However, the end is a problem because I do not have a broach. Making one is simple enough, but not in the cards just now - I have resolved that I am going to finish a bunch of projects before starting more new ones.

Thank you to everyone for your assistance !

EddyCurr
02-28-2017, 02:17 PM
I had a similar problem on a low cost chuck, decided to use it as learning opportunity. I had to make a rotary broach to get the square for the key done.

http://i1313.photobucket.com/albums/t554/boats5/918680B4-843A-4E5D-AA46-AA77EA366E3D_zpszidpkrh8.jpgNice work on the broach and cutters. I bet those are very useful tools to have on hand.

Some day ... (FWIW, the OEM operating screw has a 9/32" square socket with sides that are about 25/64" deep. This is approaching the recommended broaching depth/dia limit of 1.5:1.)

As noted by wombat2go, the socket on my Burnerd has a different shape than on his Skinner. Almost as though the four corners were drilled before Burnerd socket was broached?

http://www.slalom4me.com/imaged_a01/jpg/other/tools/lathes/SouthBend/2017.02.25_BurnerdChkOpScrew_01.jpg

vs wombat's Skinner Chuck (https://app.box.com/s/0co5to5aerf4v1xisc8adflz613pb8cg)

BCRider
02-28-2017, 03:05 PM
I can understand why they made the round pockets in the corners to reduce the risk of a stress riser. But it just seems like they removed too much material. The walls to the outer surface in those pockets is DARN THIN! ! ! !

Looking at Wombat's picture and checking my own chucks show square recesses this other method of filleting in the corners to avoid a stress riser and rounding the corners of the chuck key square ends seems like a better way.

Not that it will help you. You're stuck with the Burnerd parts for good or bad. And it's easier to just put a muzzle on the "inner gorilla" and use a little restraint when centering with that last bit of torque from here on in. Even if it wasn't you that cracked this screw it does suggest that you don't want to find out what it takes to crack another one.

old mart
02-28-2017, 03:59 PM
Hey, Eddy, I have some of those screws for the lightweight 6" acme four jaw chuck. and maybe a plug or two. At the museum, we had a poor old four jaw which turned out to have too many faults to be worth repairing. All the screws work although two have very worn threads. I got lucky and bought a new Toolmex chuck on eBay fro 1/3 the new price so the Pratt is redundant.
I would be happy to send them to you FOC
Double check that your screws are the same dimensions as the 5/6" 8tpi acme threaded ones advertised by Rotagrip.