Looking for input on adding a set screw to Stronghold chuck.......

[Odie]

As some of you may know, I specialize in thin-wall bowls. It is my usual to do the foot as the last thing prior to applying finish. For this, I use a Stronghold chuck with either Mega Jumbo Jaws, or Jumbo Jaws.

I was working on the foot of a very thin 3/32" wall bowl this morning and cracked the bowl while bringing it up to speed. (Not using tools, just increasing speed.....and, very slowly at that.) I was using the expand mode. This has happened about a dozen times in the past 5-6 years. My rules are to use light holding pressure, always slowly bring up to speed, and slowly reduce speed. This has helped, but my bowls are getting thinner and weaker. Now my rules are to ALWAYS use the contract mode, when that is possible.....which is sometimes not possible, due to shape of the bowl. Something I haven't tried yet, but will on the next application, is to use only 4 grippers, instead of 8. (I thought of using 3, but that would leave one jaw without pressure to take up the slack.)

For this bowl today, I was using very light pressure, and I'm getting to the point where I worry that the jaws might move, and fling the bowl......although, that scenario has not ever happened......yet! (knock on wood!) I'd like to use more jaw pressure, but I've actually cracked a bowl or two just mounting with too much pressure. The act of just bringing up to speed, or reducing speed is enough to crack a weak thin-wall bowl. Since nearly all bowls will warp to some degree, this is the reason why there is a problem with weak bowl walls, jaw pressure, and the physical limitations, or stress on the bowl while adjusting rpm......I believe the proper terminology that would apply to what's happening is bowl "harmonics".

OK, now what I'd like to do is add a set screw in the side of the housing. (See picture.) Sticker is placed where I'd like to add the set screw between housing and main gear. If I did this, I could use even lighter jaw pressure, without the worry that the scroll won't move while doing the foot......and, throwing the bowl into the stratosphere!

I have a question.......Does anyone know if the Stronghold chuck housing is hardened? If it is, that would be a problem for drilling a hole at that location, and probably would make threading the hole a bit difficult, as well. How can I test the hardness of the housing to know for sure? I have access to Rockwell hardness test equipment at work, but thought someone might know of a quick method using common shop/home materials.

Adding a set-screw is one thing Oneway might consider in the manufacture of their Stronghold chucks......would be easy to do. It wouldn't help most turners, but it would be a great help for my thin-wall bowls.

Any comments, thoughts and suggestions are welcome..........

Thank you......and BTW, Happy Thanksgiving to you all.......

ooc

 

[Gynia]

run a file across steel. If the file skips across the steel it is hardened. If the file starts to cut it is soft.

You can also use a pointed punch. If you can't make a mark it is hardened. If you can make a dent it is soft.

My recollection is that the newer Oneway chucks (in the last 6 years or so) use hardened jaw slides and a hardened scroll. The jaws are mild steel and the chuck body is plated, nickel I think. I know that the chuck body is milled from a solid block of steel. I seriously doubt that they harden the chuck body.

 

[hockenbery]

Oldie,
happy thanks giving . Just made the Waldorf salad.

Thin bowls can't take much pressure on the rims or side walls. It is difficult to use a rim grip or a vacuum chuck on thin bowls without cracking them.

I do almost all of my bowls on a small jamb chuck. I mount the jamb chuck in the four jaw Chuck and turn it round with a small depression, sort of a tiny bowl. One a bit under 3" diameter works for thin walled bowls up to about 12" in diameter. Thick walled bowls need wider support. I put fun foam on the jamb chuck, put the bowl over it, and bring the tail stock up. This makes a mount that sandwiches the bottom of the bowl between the tail center and the jamb chuck. Almost impossible to put enough pressure on the bowl to break anything. Then turn the bottom of the bowl and form the foot however you want it leaving a wooden pin from the tail center to the recess of the foot about a 1/2" diameter. The last thing is to turn the wooden pin thin enough to easily cut through it. on a normal face grain bowl the pin is very fragile and you can't put bevel pressure on it. I use a spindle gouge for the final work as something with a point is needed to work the pin down.

I usually leave a tiny bump on the bottom of the bowl and cut through the pin on the top of the bump to keep any fibers from pulling out when the pin is cut off with a carving gouge. I generally cut the pin to about an 1/8 thick to the cut through with a carving gouge. The bump sands away quickly with a small mandrel. Don" sand through the bottom!

Another good way to turn the bottom off a thin bowl is to use a doughnut chuck with a stand-off on the base of the doughnut chuck. The standoff can look a lot like the jamb chuck above but needs to have enough length to keep the rim of the bowl off the base of the doughnut chuck. This is a good method if you want to turn a fine detail in the bottom center of the foot.

Have fun,
Turkey Time..

Al

 

[David Wilkins]

Odie, I would suggest a different approach than to mess with your chuck. Turners tape, it's ~$10 a roll at Lee Valley and holds well. That and a piece of ply and you should be able to dampen some of those harmonics. If you have something particularly weak you could even install some bridges with hot glue.

Personally I would probably just go straight to the hot glue, but glue a block to the bottom of the bowl and the stable surfaces would be the joined ones, the outer rim under no stress. I've used both of these solutions in classroom situations and with some funky turnings, they hold better than most might consider.

 

[JerrySambrook]

To Odie, If you have the room for it, why not use a vacuum system? You cam make both different dia chucks and different length chucks to suit you needs. They are easy to make.

@Al, why is it difficult to use vaccumm on a thin bowl? If you do not apply the vacuum too fast, and if you do not try to hold to the extreme outsides, then there should not be an issue. in fact, look at the amount of surface area over the 6 inch dia, and there is typically enough force to hold most of the bowls that most of us make. If you find the bowl is flexing you can change to a slightly smaller, say 4 inch dia, chuck, or lower the vacuum pressure.

Jerry

 

[Odie]

Thanks to everyone who responded, and suggested alternative methods of mounting the bowl in preparation for turning the foot. These other methods are always a possibility for me to try, but I'd prefer to proceed with the set screw and test that theory for feasibility first. Of course, your ideas are appreciated.

run a file across steel. If the file skips across the steel it is hardened. If the file starts to cut it is soft.

You can also use a pointed punch. If you can't make a mark it is hardened. If you can make a dent it is soft.

My recollection is that the newer Oneway chucks (in the last 6 years or so) use hardened jaw slides and a hardened scroll. The jaws are mild steel and the chuck body is plated, nickel I think. I know that the chuck body is milled from a solid block of steel. I seriously doubt that they harden the chuck body.

Gynia.......I've tried a miniature file and it cut the metal of the housing. It looks like the housing is not hardened. After that, took measurements and center punched a mark at the correct location.

Just so happens, I have a 10-32 tap, and a set screw to match.......so, it looks like I'm good to go! 😀

The chuck is now disassembled and ready to drill and tap. My tap set does not have instructions for the correct size hole to drill, but I do have a 1/2" x 20 tap that is marked to use 29/64" drill. That's a full 3/64" smaller than the threads........pretty sure 3/64 smaller than the 10-32 would be too small.......anyone know the correct hole size to tap 10-32 threads.....????? 😕


I'm on my way out to the shop right now to drill a small pilot hole.

thanks, again...........

ooc

 

[Gynia]

10-32 uses a #21 drill bit. which is ever so slightly larger than 4mm.

http://bobmay.astronomy.net/misc/drillchart.htm

 

[Odie]

10-32 uses a #21 drill bit. which is ever so slightly larger than 4mm.

http://bobmay.astronomy.net/misc/drillchart.htm

Thanks for the link, Gynia........

Don't have any numbered bits here, but I do have a 5/32 which is only .00275" smaller......I wonder if that would work? Otherwise I'm stuck until the hardware store opens tomorrow........

5/32 = .15625"

#21 = .159"

OK, I'm really outa here now.......got to drill that pilot hole! ....among other things!

ooc

 

[Bill Boehme]

Since I just finished replacing a spindle adapter, I can tell you that the housing is not hardened. The screws that I used to jack the old adapter out of the housing made really large dimples where they contacted the body. It also caused the walls of the tapered surface to have a slight bulge near those two spots -- which led to more work cleaning up the bulged area. Most of the time the tapered spindle adapters are not stuck quite so tightly -- it is only because I needed to replace it that it was so tight.

Don't bother with the hardness testing since it is a destructive test.

Often the tap size is marked on the tap body. Sometimes two sizes are given depending on whether you want a tight or standard fit for the screw.

 

[hockenbery]

Jerry,

Vacuum is not my first choice for a thin bowl ( 3/16 or less wall)

Too much vacuum the thin bowl will crack.
Thin bowls are often out of round and the vacuum forces it towards round at the chuck which can crack the bowl.
Thin bowls leak more air than thick ones and pull dust into the wood.

A bowl never cracks on a jamb chuck and it it is a quicker set up than vacuum.
I use vacuum a fair amount just not on thin bowls.

I've cracked thin bowls and thin platters using vacuum. I decided it is not worth the risk touse vacuum when a jamb chuck will do the job.
This is just my opinion and my experience.

Al

 

[gary rock]

Odie

Have used the jam chucks with a piece of leather or foam then bring up the tail stock. Or when I use the mega jaws, I always put painters tape on the piece then use straping tape run up on the mega jaws or to the chuck, (when I get the feeling that this needs to be done). When I have placed the tape all the way around the piece , then the last taping is to the tape going to the chuck to make it tight. I would rather waste tape and not lose a piece.

Gary:cool2:

 

[Odie]

Howdy all........

I did a test 5/32" hole on a piece of scrap metal, and the 10-32 tap threaded the hole without any problems. My stronghold chuck now has the set screw installed, and is put back together, ready for use.

Having done many thin wall bowl footings in the past using the Stronghold chuck w/Jumbo jaws successfully, I suspect this is going to improve my batting average somewhat by using this new twist to an old tried-and-true method. I should be able to use less jaw pressure when using the expand mode, which in turn, will reduce applied stress to the bowl during this phase of completion. Probably will never be 100% fool proof, because it's the nature of thin wall bowls to be very delicate and unpredictable.

Just in case anyone else is considering using very light jaw pressure to secure a thin wall bowl to jumbo jaws......a word of caution. Do not attempt to do this, unless you can do it without the slightest mistake or catch of any kind. Your tools better be sharp, and presentation must be perfect......or your bowl will become a missile! ......ask me how I know that! Heh,heh,heh! (I know there are plenty of very experienced turners who frequent this forum, and that message isn't intended for those who are.......it's for the new turners who visit here, and there are plenty of those, too! 😀)

ooc

 

[Robin Thompson]

"Just in case anyone else is considering using very light jaw pressure to secure a thin wall bowl to jumbo jaws......a word of caution. Do not attempt to do this, unless you can do it without the slightest mistake or catch of any kind. Your tools better be sharp, and presentation must be perfect......or your bowl will become a missile! ......ask me how I know that! Heh,heh,heh! (I know there are plenty of very experienced turners who frequent this forum, and that message isn't intended for those who are.......it's for the new turners who visit here, and there are plenty of those, too! )"

I can only speak for myself here, Odie. I am not an accomplished turner and appreciate your specific advice as well as the recommendations from the other turners. I apply what I learn here on a regular basis while learning to turn; it helps.

Thanks to all and happy thanksgiving to my American neighbors.
Robin

 

[Bill Boehme]

Odie, I would recommend that you put a jam nut on that screw to keep it from backing off if there is vibration. An alernative approach is to distort the tapped hole by using a prick punch to put a dimple about one diameter away from the hole. This will result in a slight interference fit. Take care to not over-distort the hole or it will need to be re-tapped. I see that you are using a hardened screw. It might be better to use a screw that has a bit of compliance under load.

 

[Gynia]

You might consider getting a set of the Vicmark buttons. The cap head screws use a 5mm allen wrench but the threads and size of the bolt is the same as the Oneway buttons. The Vicmark buttons are taller (not as good for expansion but wonderful for compression. The shape is also much better and the red urethane rubber does not mark the bowls like the black rubber buttons which come with the Oneway jaws.

 

[Joe Greiner]

Odie, you wrote of using only 4 grippers instead of 8. I think this is a recipe for grief, because they would tend to force a wave in the bowl rim. On my first small Longworth chuck, I used only 4 buttons on a small thin-walled bowl, and it didn't survive the experience. The next version used 6 buttons; version 1 (4 buttons) has been consigned to turning large rosettes for door frames.

For insurance against orbital excursions, I wrap filament tape (not merely masking tape) from the back disk, across the bowl near the bottom and then to an opposite location on the back disk; 4 locations. Thus the chuck only provides positioning and doesn't need to be very tight, although the setscrew could lock the setting. To facilitate removal of the tape, fold a flap onto itself at each end.

With a padded tower inside, you've got a jam chuck with support directly behind the working area, with or without tailstock assist. I don't see how a vacuum chuck could improve on that.

 

[Odie]

I can only speak for myself here, Odie. I am not an accomplished turner and appreciate your specific advice as well as the recommendations from the other turners. I apply what I learn here on a regular basis while learning to turn; it helps.

Thanks to all and happy thanksgiving to my American neighbors.
Robin

You are not the the only one, Robin! .......😀

Although, next year will be the 30th year since I first started turning wood, I have learned quite a few new things since first becoming a participant in this forum.

It's also obvious that the diverse opinions here make all of this information subject to personal evaluation and acceptance......because there is a lot of disagreement. You have to "pick and choose" what information you'll accept, and what you see as valuable information, may not be held in the same regard by someone else.

The learning never really stops......I hope I never lose that state of mind, because that's the road to stagnation......😉

ooc

 

[Odie]

Odie, I would recommend that you put a jam nut on that screw to keep it from backing off if there is vibration. An alernative approach is to distort the tapped hole by using a prick punch to put a dimple about one diameter away from the hole. This will result in a slight interference fit. Take care to not over-distort the hole or it will need to be re-tapped. I see that you are using a hardened screw. It might be better to use a screw that has a bit of compliance under load.

Hi Bill.......It's kind of hard to see in my picture, but I've used a lock washer under the head of the cap screw. Hopefully, that will serve the same purpose satisfactorily, but if not......your suggestions are considerations I may revert to. Thanks.

You might consider getting a set of the Vicmark buttons. The cap head screws use a 5mm allen wrench but the threads and size of the bolt is the same as the Oneway buttons. The Vicmark buttons are taller (not as good for expansion but wonderful for compression. The shape is also much better and the red urethane rubber does not mark the bowls like the black rubber buttons which come with the Oneway jaws.

Hello Gynia........I believe the subject of marring black rubber buttons on the Stronghold chuck has come up before. I have three sets of these buttons, and none of them have ever marred one of my bowls. Best I can figure, is there must have been a batch of these rubber buttons that did mark the wood surface, so I must be one of the lucky ones to never have had to deal with that.

BTW: I have several ways to adjust the height of the rubber buttons. Longer screws, stacking the buttons, and spacer washers. It's very versatile, because I can match any specific height I need by using combinations of these things......

Odie, you wrote of using only 4 grippers instead of 8. I think this is a recipe for grief, because they would tend to force a wave in the bowl rim. On my first small Longworth chuck, I used only 4 buttons on a small thin-walled bowl, and it didn't survive the experience. The next version used 6 buttons; version 1 (4 buttons) has been consigned to turning large rosettes for door frames.

For insurance against orbital excursions, I wrap filament tape (not merely masking tape) from the back disk, across the bowl near the bottom and then to an opposite location on the back disk; 4 locations. Thus the chuck only provides positioning and doesn't need to be very tight, although the setscrew could lock the setting. To facilitate removal of the tape, fold a flap onto itself at each end.

With a padded tower inside, you've got a jam chuck with support directly behind the working area, with or without tailstock assist. I don't see how a vacuum chuck could improve on that.

Hi Joe.......At this point, I haven't experimented with four grippers yet. You could very well be right.

Please explain "filament tape", unfamiliar with this term. I believe I may try some tape on some specific bowls, but would really rather avoid anything applying pressure to the bowl, thus my resistance to use any combinations of support. I have my theories on what causes the bad vibrations, or "harmonics" with a spinning thin wall and very delicately balanced bowl......but, so far, and even though I have some evidence to support my theories, not all questions have been answered.

thanks to all......

ooc

 

[Bill Boehme]

filament tape a.k.a. strapping tape a,k.a. nylon filament reinforced tape

 

[Odie]

OK, I've now tried out the set screw on the expand mode with very light pressure, on a thin wall bowl.......worked as I'd hoped it would, but it will take multiple times to get a good idea if the concept is completely reliable, or not....... 😕

It's my theory that it's not the specific physical properties of the bowl that is the main problem (although it's certainly a significant part of the equation), but the real issue is the external forces applied to whatever internal stress the bowl may already have......that's the big problem. Theoretically, if there were zero force applied to whatever internal stress is already present within the bowl, you could probably spin a thin wall bowl on a lathe pretty fast, and nothing would happen.......I think! Obviously, "light pressure" is not the same as "zero force", but I'm getting closer to the mark with the lighter holding pressure afforded me with the use of the set screw.......results over time will give me a better idea of the value of the set screw.

Anyway, things look positive, so far......this set screw idea just might work out for my purposes! :cool2:

Note to Bill: I trimmed the set screw (cap screw) to an exact length. When snugged up tight against the chuck housing, it applies the right amount of pressure against the gear ring to prevent "drift", while at the same time, compressing the split ring lock washer. I only have to back off 1/4 turn to release the gear ring, and the split washer is still compressed. If things work as I envision them, the set screw will be permanently prevented from backing out, whether it's being used, or not........

ooc