Minimalist hollowing rig

[Frank&Earnest]

Alas, I found out that I enjoy more making tools than working wood...

Here is the last addition from the addiction: the simplest way I found to hollow my first vase.

1) insert a 1" steel rod in the tool rest and measure against the centre point.

2) cut the rod and drill at the centre point height a hole of the same size of the gouge bar, in my case 3/8" because I only have a 3/8 gouge. I have also drilled a 1/2" hole on the other end for possible future use.

The hollowing rig is done!

Photo 3 : the gouge inserted in the rig

Photo 4 : once the piece is oriented in the most convenient way, the rig provides a pivot point for the straight bar that makes easy to calculate the position of the cutting edge and therefore the sweep of the inside curve and the thickness of the wall.

Photo 5 : the final result (190h). I do not say "finished" because, not having a proper scraping tool, the inside after the neck is still rather rough.

[Barry Hicks]

F&E, that is brilliant! I am off right now to buy a piece of iron bar to make one. I have been in more strife than the early settlers trying to do some hollowing.

Barry Hicks

[Alastair]

Good thinking.

My only concern is that with nowhere to go in the event of a bad dig-in, there would be a danger of bending or breaking the gouge, or pulling the workpiece out of the chuck.

That said, it is similar in concept to the Jamieson system,
http://www.lylejamieson.com/tools/index.asp

although the mechanical advantage is probably better there.

regards

[Frank&Earnest]

Thanks Barry, good luck with yours. Let us know how it works and about your improvements. BTW: I predrilled a 1/2" hole in the centre to the desired depth, I don't know whether it actually helps. I thought it might, but I will try without next time to see the difference.

Alastair, thanks for your comments. I would have thought that the risks you mention are intrinsic to the hollowing process, are you suggesting that this rig makes them worse than they could be expected with other ways of holding the tool?

I have looked at the system in your link, but to me it looks very complicated and expensive: in which way is it similar in concept to mine? I am not claiming to have found any new concept or new tool, just a toolrest more effective for the purpose that costs only a few cents.

[Alastair]

Hi F&E

Where I was coming from, is that when deep hollowing hand held, if you dig, the tool isn't rigidly held, so the handle will be jerked up. While this could fling the tool, or cause injury, it is not rigidly held, in which case something will have to give way.

Remembering that, with internal hollowing, the start of a catch moves the cutting point down, which pushes it deeper into the rotating timber, compounding the problem. With the cutting point held rigidly, this is less likely to happen, so maybe the tendency to catch is removed, and there is no danger except in the hands of the ham-fisted.

The Jamieson system uses the same principle as yours. The tool rest at the entrance of the workpiece supports the tool, and keeps it cutting in centreline. The trap and "D" ensure that the "handle-end" cannot move up if the tip digs in, (the "D" also prevents the tool from twisting, which your design can't). In your version, both functions are performed by your vertical 'tool bar' . The fact that in the Jamieson type they are separated by a foot or so, gives better mechanical advantage.

As to expensive, someone good with tools like yourself, it would not be difficult to make. Several of our Guild members have done so. It is on my "to do" list as well. I might also have to have a whack at yours as well!!

regards

[rsser]

It would make me uneasy not to be able to see how the cutting edge of a gouge was presented to the stock (... assuming we are talking about hollowing a semi-enclosed form here).

With a scraper edge, after initial alignment with the equator, this isn't an issue. You're either in contact or not. With a gouge, you need to know where your flute wings are. A mistake here can land you in deep do-do's.

Make sense?
.

[Frank&Earnest]

It would make me uneasy not to be able to see how the cutting edge of a gouge was presented to the stock (... assuming we are talking about hollowing a semi-enclosed form here).

With a scraper edge, after initial alignment with the equator, this isn't an issue. You're either in contact or not. With a gouge, you need to know where your flute wings are. A mistake here can land you in deep do-do's.

Make sense?
.
Totally. I only did it with a gouge because I did not have anything else and wanted to go through it to prove the concept. I even thougth of sacrificing 10mm or so and regrind it as a scraper. This said, however, the inability to see the cutting tip is not too big a problem because you have good visual control of the angle of incidence and the angle of rotation of the bar. I gave it the maximum angle of incidence possible and rotated the bar 45 degrees, so that I was virtually using the wing of the gouge as a scraper. Predrilling the centre hopefully helped.

[wheelinround]

Excellent idea :2tsup::2tsup:

[Skew ChiDAMN!!]

Good idea, but needs some refinement. I agree 100% with Ern, it's not a good idea to use a gouge.

Also, with it set up that way the amount of undercutting which can be done is restricted by the angle (in the horizontal plane) that you can introduce the tool to the wood.

Something I'd look into is doing the same thing to make a 1/2" bar that'd fit your tool-post, with the hole drilled at 45° in one end to take a HSS cutting tip. One of the benefits of this would be that in a bad catch situation some of the force applied on the cutting bar would be converted to rotational force instead of "bending" force, trying to spin the bar in the post and reducing the chance of bending/snapping it.

I also think that I'd be using a double banjo set up, to reduce the stress on 'em. My banjos are only cast and I doubt that one by itself would stand up for long to the forces involved with a setup like you're proposing. :(

Hope that all makes sense? (I still think your basic idea is good, though... if I had the gear here, I'd be trying it myself! :wink:)

[Frank&Earnest]

Hi F&E

Where I was coming from, is that when deep hollowing hand held, if you dig, the tool isn't rigidly held, so the handle will be jerked up. While this could fling the tool, or cause injury, it is not rigidly held, in which case something will have to give way.

Remembering that, with internal hollowing, the start of a catch moves the cutting point down, which pushes it deeper into the rotating timber, compounding the problem. With the cutting point held rigidly, this is less likely to happen, so maybe the tendency to catch is removed, and there is no danger except in the hands of the ham-fisted.

The Jamieson system uses the same principle as yours. The tool rest at the entrance of the workpiece supports the tool, and keeps it cutting in centreline. The trap and "D" ensure that the "handle-end" cannot move up if the tip digs in, (the "D" also prevents the tool from twisting, which your design can't). In your version, both functions are performed by your vertical 'tool bar' . The fact that in the Jamieson type they are separated by a foot or so, gives better mechanical advantage.

As to expensive, someone good with tools like yourself, it would not be difficult to make. Several of our Guild members have done so. It is on my "to do" list as well. I might also have to have a whack at yours as well!!

regards

Thanks for your very clear explanation, A. a possible improvement, therefore, could be flattening the top of the round bar holding the cutting tip and putting a sort of grub screw in the top of the rest rod, to prevent twisting.

It would be really good if you and many others tried it for yourself, it would cost you only a few cents anyway!:) Then we could work out the various advantages/disadvantages.

I would certainly need a lot more attempts to see how far this method can go. From my brief initial experience I am not very worried about either of the weaknesses mentioned. The ability to twist might even add a bit of usefulness, depending on the application. As far as horizontal stability goes, I am not so sure. If the purpose of the trap and D is to stop the handle end from rising in a dig in, distance is useful only for increasing the flexibility in the bar to absorb the force exerted against the fulcrum and reduce the chance of it breaking or bending, as you said. My guess is that the advantage could be felt only in extreme circumstances.

Generally, though, I agree that you get what you pay for. An you would not pay a lot for a hole and a cut in a 1" metal rod...:D

[Frank&Earnest]

Good idea, but needs some refinement. I agree 100% with Ern, it's not a good idea to use a gouge.

Also, with it set up that way the amount of undercutting which can be done is restricted by the angle (in the horizontal plane) that you can introduce the tool to the wood.

Something I'd look into is doing the same thing to make a 1/2" bar that'd fit your tool-post, with the hole drilled at 45° in one end to take a HSS cutting tip. One of the benefits of this would be that in a bad catch situation some of the force applied on the cutting bar would be converted to rotational force instead of "bending" force, trying to spin the bar in the post and reducing the chance of bending/snapping it.

I also think that I'd be using a double banjo set up, to reduce the stress on 'em. My banjos are only cast and I doubt that one by itself would stand up for long to the forces involved with a setup like you're proposing. :(

Hope that all makes sense? (I still think your basic idea is good, though... if I had the gear here, I'd be trying it myself! :wink:)

Thanks Skew. Agree with all you said, was thinking along the same lines.
I have a feeling that the double banjo might be an overkill, though.

As far as trying one if you had the gear, just give me the measurements and I will gladly make the toolrest for you... just a small homage to show my gratitude for your great advice on these pages! Then you can experiment with any 3/8" and 1/2" bars you can find.

[Skew ChiDAMN!!]

Thanks Skew. Agree with all you said, was thinking along the same lines.
I have a feeling that the double banjo might be an overkill, though.

I dunno. It'd be OK with the amount of overhang that you have shown in the pics, but when deep hollowing there's usually a lot more of an overhang and far greater leverage than that! Don't forget that in an ordinary catch, the tool handle usually rises out of your hand, no matter how strong you are, which alleviates much of the streses involved. With a rigid setup, all of the forces will be xferred through the toolpost to the banjo... which is typically weaker than a 1" solid steel bar and is the weakest link.

My concern is that the only thing holding the post upright is the banjo, and it's not designed to take forces laterally. Especially not the repeated "hammering" a series of catches on that setup would give it. As I said, mine are only cast. Adding a second banjo would translate much of that lateral force into down force, which is what a banjo's designed to handle. ie. it becomes a fulcrum, rather than the axis of rotation.

http://www.woodworkforums.ubeaut.com.au/images/icons/icon3.gifhttp://www.woodworkforums.ubeaut.com.au/images/icons/icon3.gif Ackershully... hmmm... if you put a tool-rest in the first banjo and position it close to the work-piece, you could forget about it altogether once set up and simply advance the second banjo, with the hollowing rig, in exactly the same way as you do now. :2tsup: Fulcrum problem solved! Simple!


As far as trying one if you had the gear, just give me the measurements and I will gladly make the toolrest for you... just a small homage to show my gratefulness for your great advice on these pages! Then you can experiment with any 3/8" and 1/2" bars you can find.

Thank you! I may just take you up on that. :wink:

[Hardenfast]

http://www.woodworkforums.ubeaut.com.au/images/icons/icon3.gifhttp://www.woodworkforums.ubeaut.com.au/images/icons/icon3.gif Ackershully... hmmm... if you put a tool-rest in the first banjo and position it close to the work-piece, you could forget about it altogether once set up and simply advance the second banjo, with the hollowing rig, in exactly the same way as you do now. :2tsup: Fulcrum problem solved! Simple! :wink:

I think you may be onto something there, Skew. Sounds like a nice refinement to a simple innovation. This is what this forum does so well.

Good post and WIP Frank. Be sure you let us all know how this progresses.

Regards. Wayne

[hughie]

F&E,
It certaintly has some potential. Not so sure about the gouge though, I perhaps would use some sort of scraper.
Does the tool holder swivel? If so, it would then allow more freedom of movement and perhaps to back off in a jam up.
On some of the deep borers I have made, I fit a extra handle at 90' to control the twisting motion to date its been ok. I use a clamping method, later I intend to fit/weld a boss and screw the handle on for a greater degree of strength. The clamps tend to allow a measure of twisting..can be fun..:U

[BANNED]

Hi Frank&Earnest,

I reckon you got there, a neat, simple and economic idea, to help to hollow turning timbers. I can see all the points made by everyone, when used, but I will feel a lot more confident to advise alterations and or refinements, after I use it myself, as your original idea. So, I will be looking for some steel tomorrow, and go from there...!

Thanks, mate
Cheers
GV

[Frank&Earnest]

Hi guys. I have done a bit of thinking (that's me allright: shoot first and think later!) and following the links suggested have come to the following conclusions:

- my rig does not work at all like the Jamieson system.

- using a second banjo as suggested by Skew would only result in a less effective version of the Jamieson system - it would then be better to make one that way as suggested by Alastair.

- my rig works exactly like Vermec's "Ultimate Hollowing Tool" system. Any weaknesses of my simplified version would also be the weaknesses of that system. I would even suggest that because in my design the fulcrum is coaxial to the banjo the lateral stress is smaller.

- the banjo of the Vermec lathe in the photos looks flimsier than the Jet banjo I am using. Can't be sure on such poor evidence, but I am happy to take the risk. I assume (yes, I know, I know :) ) that they have done their homework and their system works, so why would not mine?

When all is said and done, the proof of the pudding is in the eating. Will try to get a proper hollowing tool and to push it up to 350mm deep to see what happens.

[ticklingmedusa]

Frank & Ernest, interesting idea.
Check this link out it might give you some ideas.
www.elbotool.com (http://www.elbotool.com)
I "test drove" one at a turners symposium and it worked a treat.
tm

[Fredo]

Frank & Ernest: Er... not totally convinced. The deeper you cut the more load would be placed on the upright bar through the tool hole. Does the tool tend to stick or jam as you push it through? Anyhow, keep up the R & D work. It's a nice idea and is simple to make if you can get it to work well. (As suggested by others a HSS cutting tool on a steel bar works). Good luck with it.

I have a couple of home brew hollowers, this one (pics) is a cross between the elbotool (see TM's post) and the Vicmarc tool. The main tool is easy to make but the rotating upright is very complicated to home brew. Overall this tool works very well.

I have experimented with cutters, the Munroe blade and HSS tip on a bright steel bar. I find they all work effectively. Laser guide helps.


Fredo

[Frank&Earnest]

Hi TM and Fredo. Thanks for the reference to this other system. I have looked at the link, which explains what is rather self-evident in the photos:

"It is fastened to the quill in the tailstock by a clamping system to restrain the tool in all but the horizontal plain. "

This and the Jamieson system would then reduce the problem of the vertical stress at the cutting edge becoming a lateral stress on the banjo.
The problem of the bar potentially bending or breaking (in this design probably at the joints) or the piece being wrenched off the chuck seems to be common to all designs.

The Vermec system and my design, that now can be aptly described as a crude approximation of that, do not restrain the bar from rotating (which is controlled by adding a handle at a 90 degrees angle, as hughie also suggested) and offer less protection from lateral stress on the banjo. They both allow to swivel the bar horizontally and my design also allows to block the swivel, if desired, by tightening the toolrest blocking screw.

The main question now is: does the Vermec system work well? If it does, my simplification can do a substantial part of, if not all, what it does for a fraction of the cost. If it does not, my simplification would only be a cheap solution with a limited range of usefulness. Comments from everybody on experiences with the Vermec would be most useful.

Fredo, compliments on the professional quality of your hollower. Unfortunately, because I do not have the skills and the tools for metalwork, I am only limited to simplifications, not improvements...:-

[BANNED]

Hi everyone,

Yeah, I agree with Frank about the professional quality of Fredo's hollowing jig. Is a fair amount of work and brains involved into fabricate a jig like that, and appears to works very well so, a nice icing in the cake.

Some day, I will thing in get/make/buy one like that!
In the mean time, I got today a piece 2 feet long of stainless steel pipe, just the right size for my banjo. This go to allow me to follow Frank's original idea, as a starting point! will see...!:-

Cheers
GV