Thread: Minimalist hollowing rig

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

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

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.

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

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?
.

Originally Posted by 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?
.

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.

Excellent idea

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! )

Originally Posted by 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

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...

Originally Posted by 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! )

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.

Originally Posted by Frank&Earnest

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.

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. 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.

Originally Posted by Skew ChiDAMN!!

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. Fulcrum problem solved! Simple!

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

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..

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