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View Full Version : New(?) tool concept - could it work?



Skew ChiDAMN!!
28th Jul 2009, 07:47 PM
I've long had an idea for a piece I'd like to make quite a few of, but production turning isn't really my thing. (They need to be fairly accurate and I don't really want to throw away two out of three attempts. :B)

However, after mulling over a discussion in another recent thread while playing on the lathe, I've had an idea which could possibly speed things up & reduce failures.

Part of what I want to do will involve the turning of a lot of domed disks, so I'm thinking of turning a large, domed jig on a faceplate. About 24" dia. with a dome radius of around 36" Then turning recesses at offset positions in this jig that I can jam-chuck several smaller blanks into, for simultaneous turning.

In theory I can simply turn the blanks down to be flush with the jig and they'll be right to use. However, with every use a bit of the jig will be turned away so that after a few uses it'll be of different radius and need to be replaced.

Or will it? That's my problem & I'm wondering if the following tool will extend the life of the jig.

Imagine a, let's say, 1/2" skew chisel. Blunt the cutting edge, rolling it over to form a curve of only 1mm or radius or so.

Then grind the bottom bevel back on, across the full width. Next, grind the top bevel back on, but only on the left half of the top. ie. so the edge of the grinding wheel is in the middle of the chisel, leaving a step.

Finally, use a hone to lightly round over the intersection of the bottom bevel and the unground portion of the top part. So that it won't cut in a blue fit.

The idea being that this blunted RH side of the tool will act like a router-bit bearing does when template cutting.

You'd rest the RH side of the tool in the middle of the jig and make cut towards the outside, following the jig profile. The LH side will cut and the RH side will ride over the cut section, continuing to act as a guide.

I'd imagine that it'd wouldn't automatically follow the profile, cutting off on a tangent if you hold the tools traight, but you could control the cut by gently rolling the tool. Just like turning the outside of a bowl, really, 'cept it's only cutting high spots.

Does anybody follow what I'm on about? Does it make sense or am I missing something obvious? I don't really want to lose either the time - or tool steel - by regrinding one of my good skews just to find it won't work because of something that I should've seen straight off the bat.

(I have enough of thoe moments as it is! :rolleyes:)

jefferson
28th Jul 2009, 08:03 PM
Andy, DJ's got this cutting jig from Vermec that should do the job. I've seen the beast in use for the tops of grinders and it does a wonderful, repeatable job.

Where are you DJ's Wood?

robbiebgraham
28th Jul 2009, 08:12 PM
Personally I can't see how you can turn more that one domed disc in a jig because the centre of the dome needs to run on the centre of you face plate. Soon as you move them off centre they no longer are domed. That's if I under stand what you are saying!!!!
A diagram of what you want to do would show us your intention and be easier to under stand.
Robbie

Skew ChiDAMN!!
28th Jul 2009, 08:23 PM
The curvature on a sphere is the same at any point. That's part of the definition of a sphere being a sphere and not an ovoid.

Imagine a 3' sphere, drawing a 2' circle on the surface and cutting that out to use as the jig.

Every part of that jig's surface will have the same curvature, even when it's spun in a lathe. It would have to be mounted precisely to eliminate wobble, of course, but as it'd actually be turned from a block of wood and not cut out of a sphere, that's not a problem.

Then I can cut mortices, say 6" diameter, in the jig to jam-chuck 6" blanks. They can be randomly positioned to fit as many on as possible, because the curvature is the same all over. ie. they don't have to be in the centre to be cut with the same dome. :)

This is only true for a sphere (or part thereof) though.

robbiebgraham
28th Jul 2009, 08:32 PM
OK. I under stand what you are trying to do now:doh:

RETIRED
28th Jul 2009, 08:34 PM
Imagine a, let's say, 1/2" skew chisel. Blunt the cutting edge, rolling it over to form a curve of only 1mm or radius or so.

Then grind the bottom bevel back on, across the full width. Next, grind the top bevel back on, but only on the left half of the top. ie. so the edge of the grinding wheel is in the middle of the chisel, leaving a step.

Finally, use a hone to lightly round over the intersection of the bottom bevel and the unground portion of the top part. So that it won't cut in a blue fit.

The idea being that this blunted RH side of the tool will act like a router-bit bearing does when template cutting.

You'd rest the RH side of the tool in the middle of the jig and make cut towards the outside, following the jig profile. The LH side will cut and the RH side will ride over the cut section, continuing to act as a guide.

I'd imagine that it'd wouldn't automatically follow the profile, cutting off on a tangent if you hold the tools traight, but you could control the cut by gently rolling the tool. Just like turning the outside of a bowl, really, 'cept it's only cutting high spots.

Does anybody follow what I'm on about? Does it make sense or am I missing something obvious? I don't really want to lose either the time - or tool steel - by regrinding one of my good skews just to find it won't work because of something that I should've seen straight off the bat.

(I have enough of thoe moments as it is! :rolleyes:) I think I see what you are trying to do and doubt that it work for the following reason.

Because you have a step it will "catch" on the turned section as soon as it reaches it.

Try using a bit of flat steel and see how it goes on a small scale first.

tea lady
28th Jul 2009, 08:40 PM
:think: Sounds like a lot of work to not do some work. :shrug: How are you gonna cut all the other little circles on the dome? :?

Skew ChiDAMN!!
28th Jul 2009, 08:57 PM
I just want plain, domed disks. I'm not trying to copy Ken. :)

They'll be 15(D) x 1(T)cm Huon & Tas. Myrtle, actually. A bit over 200 of 'em. If I can turn four at a time, that's only 1/4 of the time to do 'em individually.

Calm
28th Jul 2009, 09:37 PM
I just want plain, domed disks. I'm not trying to copy Ken. :)

They'll be 15(D) x 1(T)cm Huon & Tas. Myrtle, actually. A bit over 200 of 'em. If I can turn four at a time, that's only 1/4 of the time to do 'em individually.

If you made a curved rest the shape you want and mounted a long blank in my Titan chuck you could follow the rest - part off, follow the rest, part off, follow the rest i think you get the picture.

Cheers

RETIRED
28th Jul 2009, 09:39 PM
Parting off 150mm cleanly is a hard task.

Calm
28th Jul 2009, 09:51 PM
Parting off 150mm cleanly is a hard task.

Part off 25mm then finish with the bandsaw???:?

Cheers

Skew ChiDAMN!!
28th Jul 2009, 10:00 PM
That's what I was thinking when I first had the idea, about a year ago. I tried parting & cutting as you suggest,Dave, then flattening the back on a linisher.

It's do-able, but a lot of effort to get right. It only takes a bit of pressure on one edge of the disk for the back to round over or cause a taper.

So I wrote off that method and have been pondering over alternatives ever since.

Calm
28th Jul 2009, 10:34 PM
Ok so do them all then clean up the cut with a vacuum chuck??

I know i'm just trying here. (very trying)

Cheers

joe greiner
28th Jul 2009, 11:10 PM
OK. I under stand what you are trying to do now:doh:
I certainly don't.:-

Any off-axis turning will make a torus, not a sphere, regardless of how the blanks are supported.

If you want precise spherical domes, with the least amount of fiddling about and clean flat bottoms, I think you need to do them one at a time. I'd consider a flat waste block holding the blanks with a glue-and-paper joint. Use a sphere-cutting jig, with the cutter mounted for a slicing cut, and cut just barely into the waste block. Prying the joint loose would damage the work, so it might be better to glue only a thin circle at the final boundary, and use compressed air through the headstock spindle (with an access hole in the waste block.

Just thinking out loud, and your final objective isn't entirely clear.:?:?

Cheers,
Joe

tea lady
28th Jul 2009, 11:19 PM
I reckon double sided tape chuck would be the go. Or a very shallow screw chuck. Just get into a rhytme. Won't take that long, and be the end you will be really good at plain domes.:cool:

So what are they for? Go on tell us, tell us.:D

Skew ChiDAMN!!
28th Jul 2009, 11:32 PM
I certainly don't.:-

Any off-axis turning will make a torus, not a sphere, regardless of how the blanks are supported.

Wrong. :) If I turned a perfect sphere, then drilled a hole in it, plugged it with a dowel & turned it back to the same curve (using the rest of the sphere as a guide) the dowel's end won't suddenly become a torus. It'll have the same curve as the rest of the sphere; a spherical dome.

I know that that part of the concept works; I've done similar before. It's the tool itself (to speed things along) that's giving me trouble.


Use a sphere-cutting jig, with the cutter mounted for a slicing cut, and cut just barely into the waste block. Prying the joint loose would damage the work, so it might be better to glue only a thin circle at the final boundary, and use compressed air through the headstock spindle (with an access hole in the waste block.

But will a sphere cutting jig handle a 3' radius?
Just thinking out loud, and your final objective isn't entirely clear.:?:?

I want to make a bit over 200 identically domed disks of 6" approx diameter and only about 8mm thicker at the highest part of the arc; the sphere radius will be some 18" so they'll only be shallow domes.

Well... that's not quite true. They'll actually have a rim thickness of about 3mm, so they'll be 11mm at the thickest point. But that's irrelevant to the calculation of the arc. :)


I reckon double sided tape chuck would be the go. Or a very shallow screw chuck. Just get into a rhytme. Won't take that long, and be the end you will be really good at plain domes.:cool:

Hehe. I've no burning desire to copy either. :D However, that might end up being the case yet. Or a simple jam-chuck to do one at a time.


So what are they for? Go on tell us, tell us.:D

Now that'd be telling! Would you be satisfied if I said... "art?" :U:B

rsser
29th Jul 2009, 06:44 AM
Tendering for textured footpaths for the blind Skew? ;-}

robbiebgraham
29th Jul 2009, 07:29 AM
I just want plain, domed disks. I'm not trying to copy Ken. :)

They'll be 15(D) x 1(T)cm Huon & Tas. Myrtle, actually. A bit over 200 of 'em. If I can turn four at a time, that's only 1/4 of the time to do 'em individually.
I once was a production turner (sounds like the start to a story) and I would do big runs and I think it would be better just to turn them. By the time you have made the setup you would probably have the job done.
Robbie

RETIRED
29th Jul 2009, 08:12 AM
I would probably turn them as well. Tea lady beat me with the double sided tape but I was thinking along those lines with a combination of double sided tape fitted in a jam chuck.

To get them into a jam chuck they would have to be cut accurately to start with.

Or a vacuum chuck in combination with a jam chuck.

Calm
29th Jul 2009, 09:11 AM
Skew the big Titan chuck is on offer if you need it.

Cheers

tea lady
29th Jul 2009, 10:29 AM
Now that'd be telling! Would you be satisfied if I said... "art?" :U:B

No! Still not satisfied. :p

If we had set ups on all of 's lathes we could do them in a day at the next turnfest!:cool:

Texian
29th Jul 2009, 02:34 PM
Maybe I missed it but seems like there might be a problem with grain orientation if turning with a skew. And as mentioned, the set up time for multiple fixture might not save much time. I like the idea of a single cavity vacuum jam chuck with very thin gasket material, and a "calibrated" sphere-turning jig/fixture. Just some more thoughts. Interesting problem.

KenW
29th Jul 2009, 03:22 PM
Skew, I understand your concept, I turned the carriage wheels a similar way, only one at a time. The sphere will take a long time to make. You don't need a special tool, a bowl gouge is all you will need. If you make the sphere a bright colour, you will be able to see it's ghost as it turns. Just turn to the ghost. If you touch the sphere with your gouge the colour will change, and you will know to change direction.
Having said all that, I would make them one at a time.
Make an accurate template. Glue your blank on to a small wooden faceplate with hotmelt glue, turn shape with dowl gouge and check shape with template, skim any high spots with scraper. Getting the shape correct won't take long after you have made a few. When disk is finished, give a a tap with you hand, it will come off easily and then fit next blank.

joe greiner
29th Jul 2009, 03:24 PM
G'day, Andy.

1. I stand corrected about the spherical surface, but you'd need to turn the blanks first to fit in the holes. Then you face the problem of slicing the backs flat.

2. The sphere-cutting jig needs only a 18-inch radius. But that would mean at least 18-inch projection from the headstock, and a steady to support the workpiece. Alternatively, the sphere-cutter could ride in a curved track toward the tailstock.

3. Robbie mentions the bother of setting up for the multiple objective. It might (just barely) make sense for 2,000 or 20,000; but not for only 200.

Grain orientation also comes to mind. And also reverts to blank preparation. Cross-grain planks would be suitable for the arrangement I first suggested, but nip the rim to the desired thickness. And a vacuum chuck would probably be quicker; also applicable to other projects, so it isn't project-specific.

I don't care what they're for. That would open up too many more cans of worms.

I'll sleep on it some more.

G'night,
Joe

Skew ChiDAMN!!
29th Jul 2009, 05:39 PM
Still mulling over the idea at work today, I mentioned it during a chat over lunch with the site's tiler/stonemason. He's semi-retired and slow as a wet weed, but he takes pride in his work and does a beautiful job. Anyway, he showed a bit of interest, asking questions about the how's and why's, so I was happy to explain. :)

At knock-off he wandered over and asked me "does it really have to be turned on a lathe?" I must've looked puzzled, because he added that he makes decorations like that out of marble and granite fairly regularly... for tombstones! Then he carves them, but to dome the blank he just uses a pivoting dop and a wet-grinder. "Why not do the same with a disk linisher?"

:woot: He rocks! That'd take all error out of it.

So no lathe needed for this job. I don't know if that's a good or bad thing, but...


(I'm still going to try making the tool I described; just to see if it has even a remote chance of working. But now that project can go into the round tuit pile... )

underfoot
29th Jul 2009, 08:38 PM
Would you be satisfied if I said... "art?" :U:B
I'd be ok with that, after all ......what else is there?

joe greiner
29th Jul 2009, 10:18 PM
Still mulling over the idea at work today, I mentioned it during a chat over lunch with the site's tiler/stonemason. He's semi-retired and slow as a wet weed, but he takes pride in his work and does a beautiful job. Anyway, he showed a bit of interest, asking questions about the how's and why's, so I was happy to explain. :)

At knock-off he wandered over and asked me "does it really have to be turned on a lathe?" I must've looked puzzled, because he added that he makes decorations like that out of marble and granite fairly regularly... for tombstones! Then he carves them, but to dome the blank he just uses a pivoting dop and a wet-grinder. "Why not do the same with a disk linisher?"

:woot: He rocks! That'd take all error out of it.

So no lathe needed for this job. I don't know if that's a good or bad thing, but...


(I'm still going to try making the tool I described; just to see if it has even a remote chance of working. But now that project can go into the round tuit pile... )
Good grief! All I did was sleep for a while, and now it's dead?

Call it a "lathe" or not, a turntable in combination with a disk or belt sander could do it. Maybe a Lancelot or Arbortech, too.

But, to maximize production, consider borrowing an apocryphal idea from NASA project managers: To produce a baby rapidly, assign 9 mothers and complete the work in one month. The joke could be applied to any agency, of course; it's mostly a dig at "management." So, divide the work amongst 20-40 colleagues, and let each create their own process, for a total of about 250 pieces to account for rejects.

Managing engineers is about as close as I've got to herding cats. Managing a team of woodturners probably isn't much easier. For you, that is.

I said I'd sleep on it, didn't I?

Cheers,
Joe

tea lady
29th Jul 2009, 11:38 PM
:think I reckon something like a bowl saver could do it. :shrug:

How about a cnc machine? But you can't call it art if you move to far from people actually doing anything.:doh:

TTIT
29th Jul 2009, 11:48 PM
............... to dome the blank he just uses a pivoting dop and a wet-grinder. "Why not do the same with a disk linisher?"

:woot: He rocks! That'd take all error out of it.

.............Ain't it cool when the best solution ends up being the simplest :2tsup:

Skew ChiDAMN!!
29th Jul 2009, 11:51 PM
Ain't it cool when the best solution ends up being the simplest :2tsup:

Too right. :) I'll still have to do 'em one by one, but the process should be fast and not require much attention. Well... not as much as accurately turning to a given profile, anyway.


:think I reckon something like a bowl saver could do it. :shrug:

How about a cnc machine? But you can't call it art if you move to far from people actually doing anything.:doh:

The dop and disk linisher is almost idiot proof. And should be easy to set up. (Bonus!)

It's basically a case of bolting a linisher to the bench, then bolting a pivot point - I'll probably make a universal joint in a frame, so I can re-use it if I ever need it again - as far away from the linisher as I want the dome radius.

Connect one end of a rod to the pivot, with the blank mounted on the other end somehow. I'm thinking a faceplate with a loose-fitting jam chuck (to easily centre the disks) and double-sided tape to hold them in place.

Then even a child could just wobble the rod around so the linisher grinds the blank to a dome shape. Think of it as an oversize Woodcut grinding jig for domes instead of chisels. But even simpler, as it's the same grind "all over" instead of needing to eyeball the wings. :2tsup:

When I get around t building it I'll post photos.

Skew ChiDAMN!!
29th Jul 2009, 11:57 PM
Good grief! All I did was sleep for a while, and now it's dead?

Dead? No, I wouldn't say that. Just... moved on... :D

rodent
7th Aug 2009, 11:40 PM
Dead? No, I wouldn't say that. Just... moved on... :D
Drew Drew Daaa david springett's woodturning wizardry page 27 upsized . See tony smith get a couple of the 27 video recorders he has , pull the video heads put in lathe machine flat . Ask me for a lone of my electric iron . Put alloy head on iron ( turn it on ) hot melt glue put on wood . Take off iorn let cool .put in lathe machine up . ps ive got a small 8 inch Less tool no handle to put the toolsteel in want to borrow that too ?:doh:

Skew ChiDAMN!!
7th Aug 2009, 11:45 PM
Drew Drew Daaa david springett's woodturning wizardry page 27 upsized . See tony smith get a couple of the 27 video recorders he has , pull the video heads put in lathe machine flat . Ask me for a lone of my electric iron . Put alloy head on iron ( turn it on ) hot melt glue put on wood . Take off iorn let cool .put in lathe machine up . ps ive got a small 8 inch Less tool no handle to put the toolsteel in want to borrow that too ?:doh:

I've already got a couple of vid-heads for use as spigots, Rod. :;

rodent
7th Aug 2009, 11:47 PM
I've already got a couple of vid-heads for use as spigots, Rod. :;do you need the tool holder as well , it's a short un handled version of Less white's tool I use it in my dogs ball jig .

Skew ChiDAMN!!
7th Aug 2009, 11:58 PM
Nar, I'll just dop 'em up and use the linisher. That way they'll all have exactly the same profile with no effort.

rodent
8th Aug 2009, 12:10 AM
OK . dont forget ( HA ! ) I have to drop some red gum off for tea lady next week >