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Building a Deep hollowing rig question ?

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I have a friend thats a retired finish carpenter and has been wanting to help me build a hollowing rig for deeper turnings and all I would have to do is buy the metal and parts. I think he is just bored and wants a project ....LOL........

I have been putting the idea off for quit some time because I have hollowing rig from Monster tools that works great for all my vessels that i currently turn (I have a Jet 1642, 2hp, 16" swing lathe) and haven't really had the need for a bigger setup. However, I have someone that wants a large vessel/vase now so I thought I may give this a try but ran into a few questions that I was unable to find answers to. So I thought I would turn to you turners that have these setup for some advice........

The first decision was to make either a "D" arm type hollowing rig or a articulated one. After quit a bit of reading I thought the D arm would be the better one to make because it seemed to be eaiser to make and alot of turners seem to use this setup for hollowing deeper vessels.

It was easy to put the drawing down on paper but the dimensions is what I am missing now. I see alot of home made rigs on the web but the dimensions were always missing......
I have it layed out with the idea of using 1" solid bar stock for the frame (most can be bought as scrap so I thought why not make it strong. It would have a 1/2" hole drilled in the front of the 1" bar so I can put adapters on to go down to 3/4" or whatever I needed.

But, then one turner on the web commented that you can make the frame out of hollow square steel because the stability is in the bar itself which should be solid - so make the rest of the frame light weight. Thoughts??
Questions::::: Should the frame be solid or hollow ?
Any idea on the dimensions I should use or a website or page that shows the layout with dimensions ?
Just wanting to get this right on the first go around = thank you ahead of time for any help and thoughts you may have......
 

john lucas

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Here's my thoughts because I am considering the same thing. I've read several times that square tubing is stronger and this isn't just from wood turners so I think it might be correct. If anyone knows for sure I'd love to know. I'm going with 1 1/2" square tubing for the main bar.
Currently my boring bars are 3/4" and they start to chatter at 12". I've hollowed up to 16" but you really have to take light cuts. I'm going to make adapters for the square tubing that will take various sizes of round or square tubing. A 1" round bar will probably go as deep as I ever plan to go but I thought I would build pieces for larger or even build an extension for the 1 1/2" square tubing to go really deep.
I may never go that deep but since I would have to blow a weekend building all this stuff I might as well build all I'll ever think I need. It won't take much longer to make the other adaptors.
 

Steve Worcester

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Round bar or tubing has less friction sliding through the gate. I use round bar and put (in this case) a 1/ 1/2" piece of bar on the end with a 1" hole on each end. You can slide that on the nose, weld it and use 1" tools.
If you are going over about 12-16" I would go with a more rigidly attached 1" boring bar.

As far as dimensions, unless you are going to have different length bars, you want to have a D section closer to the depth you want to attain. You can move the gate closer to get more length though.
 
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John - can you explain how you are going to do your adapters in more
detail ??

What I thought of originally was to have the piece comming out the front (that holds the cutting bar) be a 1 or 1 1/4 round solid bar - then drill a 1/2 hole in it down about 2" - then drill two 5/16 holes for set screws on the bar to hold the cutting bar (tool) in place.
From there make adapter that would accomadate different bars.....

Thoughts ?
 
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Here's my thoughts because I am considering the same thing. I've read several times that square tubing is stronger and this isn't just from wood turners so I think it might be correct. If anyone knows for sure I'd love to know. I'm going with 1 1/2" square tubing for the main bar.

John, Some thing to consider is sq tube wall thickness, go for the heaviest available as this will add to the stability of the main bar. Also consider a Irons Gate type tool rest for those really deep hollow vessels. This will allow you the luxury of a lighter main bar at times whilst proving max support.
 

john lucas

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Dan I'll probably use a 3/4" hole bored the actual adaptor and then adapt this piece to whatever large tubing I'll use. I haven't planned it in detail yet because it's a future project but my thoughts were to make a couple of square plates that fit inside the square tubing. Weld these together with some 1 1/4" rod that I have. My other thought was to simply get a short piece of solid square bar. Mill that down to fit the square tubing and bore it for a 3/4" hole.
All of the thick bars that I make will then have a 3/4" round tenon either turned on one end or welded on if the bar I use won't fit on my metal lathe.
 
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Sudol hollowing rig

I have an original Frank Sudol hollowing rig (below is a picture of Frank using the one I have! It was purchased after his demo.). The solid round bar is 1.5" diameter X 6' long. It has a 3/4" hole counterbored in the end. There are 3 cutters (straight, 22.5 and 45) that mount by securing them into the 3/4" hole using set screws. I can hollow about 20" to 22" before the vibration gets to be too much.

A unique feature of the Sudol system is the free standing capture rest. It sets on the floor independently from the lathe. It has a roller the hollowing bar rests on and an adjustable top bar. This is nice since the bar weighs over 40lbs. It's so easy to move that I have made mistakes with it. I was turning a vessel with 1/16th" wall thickness for piercing. I moved the tool back to blow out some shavings and when I moved the tool back into position to continue working the momentum of the heavy tool took it beyond where I wanted to stop and ruined the vessell. It took it to less than 1/16" and I could see much more light through the area I messed up. I had to abandon the vessell and start over.

Some guys I know recently built a similar rig with (I think) a 2.5" solid bar. They went to about 45" deep.

I discourage you from using a hollow tube. Also, the rule of thumb I was always told is you can go 15X the diameter (of a solid round bar) past the tool rest. So if you have a 1" bar you can go 15" beyond the tool rest. NOTE: The tool rest is very important too. The one I use with my Sudol and with my Kobra are each 1" diameter and have controlled height adjustment and have tabs at each end so you don't accidently run the tool off the end. The tabs prevent the user from making a huge, and possibly dangerous, mistake.

Don Geiger
 

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john lucas

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Don I used the Sudol rig when I took a 1 day class with him. One thing I remember is it was extremely heavy to mount and unmount from the lathe. I do remember turning a 14" deep vessel extremely thin was virtually effortless.
My first experiment will probably be hollow pipe because I already have it and it was free. I think it's about an inch and half with thick walls. I thought it would make a good first test and if it does all I need I may not go to the bigger one.
I'm still interested to know if any engineer types can tell me if a hollow bar has less flex than solid. I have heard that a couple of times but don't remember the source so I can't say if it's true. I also wondered if I filled it with something if that would reduce the vibration. I filled the hollow aluminum tube I use for my laser with Great stuff Foam and it cut the vibration tremendously.
 
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My first experiment will probably be hollow pipe because I already have it and it was free. I think it's about an inch and half with thick walls. I thought it would make a good first test and if it does all I need I may not go to the bigger one.
I'm still interested to know if any engineer types can tell me if a hollow bar has less flex than solid. I have heard that a couple of times but don't remember the source so I can't say if it's true. I also wondered if I filled it with something if that would reduce the vibration. I filled the hollow aluminum tube I use for my laser with Great stuff Foam and it cut the vibration tremendously.

In similar materials, your tube is the most efficient form for resisting deflection in any direction. If the load is limited to one direction, the ubiquitous I beam is the answer. http://en.wikipedia.org/wiki/Beam_(structure) Scroll down to "General Shapes." Not to infer that the solid is inferior, merely that it doesn't hold up in the load wt/beam wt efficiency equation.
 
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A rule of thumb in structural engineering (my former day job) is "When in doubt, make it stout."

The stiffness (Moment of Inertia) of a solid square bar is d^4/12. The stiffness of a hollow bar is reduced by the stiffness of the absent material. Stiffness is needed most in the region near the tool rest, at all positions of engagement. The remaining material is needed only to stabilize everything. So, I'd go with hollow bar for the D-section, except for the region near the tool rest. If the solid bar can telescope into the hollow, a few plug welds should be sufficient for assembly.

Round versus square: For round, the stiffness is PI*d^4/64, about half the stiffness of square. But for the D-section, threaded pipe fittings could simplify assembly.
 
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I am in the process of making a D handle system as we speak. For the main D handle I have used a heavy walled square tubing (1 1/4" outside wall and
1" Id). I then made two 8 to 10 inch long reducer and expander out of square tubing to accomodate different bar sizes. Without the reducer/expander the main bar will take a 1" bar. With the reducer tube it slides into the main bar about 4 to 5 inches and will then take a 3/4" bar. With the expander it slides over the main bar about 4 to 5 inches and will handle a 1 1/4" bar. My question after reading the posts is do you think there may be a flaw in my design or do you feel it will work. Note when the expander/reducer are applied to the main bar they have four bolts holding it to the main bar and four bolts holding the round cutting bar. Thanks for your input.

Dale
 
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Deep Boring

Greetings,
I've been wanting to make a deep boring bar system for some time now, and this thread is quite helpful and inspiring. I'd like to be able to hollow to 24" deep, was thinking 1 1/2" to 1 3/4" dia. bar (?) and also wondering what kind of steel to use for the bar, stainless or is a mild or weldable steel adequate?
I've been using a big Jamison bar and have gone to 20",with a lot of noise /vibration, and is max for me.
Thanks for helping.
M
 
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Im still trying to see if some one can give some help on the dimensions but im thinking that cold rolled would be fine for the frame.......see what others think
 
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A square tube is not stiffer than a solid square of the same dimensions.

A square tube with larger dimensions that has the same weight as a solid square of smaller dimension is stiffer. The same holds true for round sections.

I considered using square tube when building my captured bar system, but opted for round stock for the d-handle as well as the capture bar. The thinking was the reduced area of contact between the two round sections. If all parts were made from square or rectangular sections, the area of contact between the parts would be much larger, and the thinking was that that increased area would have increased drag.

I used 3/4 cold rolled througout, and with a bit of wax, movement requires little effort, and the weight of the parts is managable. To do over, a piece of DOM tubing with a 3/4" or 1" ID and a 5/16" or 3/8" wall thickness would probably be used for the D handle, still sticking with the 3/4" Cold rolled for the capture bar. The use of the DOM would add some stiffness to the system behind the tool rest, but primarily would allow for sliding the boring bars into the D handle to reduce the amount of capture bar required for getting up under the shoulder on vessels with small openings and relatively flat tops.

Later,
Dale M
 

Steve Worcester

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I'm thinking that if you rotate the square tubing 45 degrees so the corners are the contact area, it will be nearly the same as the round.

Yep, would work great, but would require you to "fishmouth/notch" the tubes to mate them for welding. That may be a difficult profile.
 
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I do a fair amount of hollow turning. I used angle iron for the tool rest that the bar rests on. 3/4" cold rolled for the D section. 1 1/4" cold rolled section 3" long bored and press fit/welded into the bar closest to the turning. This piece is bored with 2 set screws to accept a number of different tools on the business end. It works great. No torque. I made a laser light attachment. USE SQUARE TUBE The first one I made was out of round bar. I bumped it by mistake, moving the laser, and had my one and only hole in my turning. As you go deeper into the form you will find that you may need to increase the diameter of the attachment to get rid of flex/chatter. Good luck
 

Dennis J Gooding

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There are some interesting trade-offs here. As Joe Greiner pointed out the stiffness of a solid rod is proportional to the fourth power of its diameter. Also the weight of a solid rod is proportional to the square of its diameter. The values for a pipe of the same outside diameter these same values less the corresponding values for material that must be omitted to convert the rod to a pipe. Make sense?

Now suppose we had a choice of a 1-inch diameter rod or a pipe with a 1-inch inside diameter and 1/8th-inch wall thickness. If you go through the arithmetic you will find that the pipe would be 44% stiffer and would weigh only 56% as much.

If I were making a big bar where weight/inertia would be a significant consideration, I would choose the pipe.
 
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As usual, there's no perfect answer, until you do some arithmetic, like Dennis did, and draw some cartoons.

FWIW, the stiffness of a square, or a hollow square, at 45 degrees, is the same as if it were flat. So there's no stiffness penalty for the diagonal arrangement, and a benefit in the point contact.

Another item worth considering is that the cross-pieces of the D-section don't have to be the same as the longitudinals, as long as they're not larger. That can simplify the fishmouth detail, e.g. all on one side of the sloping face of the diagonal main bars/tubes.
 
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