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  #1  
Old Tue 22 September 2009, 00:47
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Structural design of an Indexer Valley

Have seen some indexer valley designs over the years and it seems there are some misunderstandings about the need for braces/gussets:


Joints A and B carry exactly the same loads as each other. Because they are nearer to the center of the table, they carry a lot higher bending load than D and C.

The indexer valley adds a lot of flexibility to the table structure because it lengthens the cross support channels. The vertical distances AB and CD are also extra length for a flexibilty calculation.

To counteract the extra length, one can add extra "depth" to the cross-supports, in as many places as possible.

With our typical DIY weld quality, our joints are weak. However, this has a small effect on flexibility, but a high chance of cracking and sudden failure. The joints at A and B would be the most critical welds on the table......if they are not braced/gusseted. It is odd that most people only brace joint A, while joint B needs just as much bracing to prevent weld failure.

Another observation is that indexer valleys are for round workpieces, but everybody seems to give them square inside corners . . . .

A very simple and efficient bracing is shown at the bottom of the diagram. This is only mentioned as an idea to get people talking and thinking outside of the typical.

Last edited by Gerald D; Fri 20 August 2010 at 21:45.. Reason: spell
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  #2  
Old Tue 22 September 2009, 03:37
ifffff
Just call me: Ivo #38 & #130
 
Parnu
Estonia
I put here my indexer valley picture too. But reason why inside are square corners is that there i have extra depht for working. Who knows what do i need to do on my mechmate.
For welding i suggest grind edges a little down and use max current.
Attached Images
File Type: jpg Indexer.JPG (8.6 KB, 1463 views)
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  #3  
Old Tue 22 September 2009, 14:10
Appimate
Just call me: Ed
 
NSW
Australia
Bracing

Hello Gerald / Group

In the spirit of thoughtfull discussion, would a better approach be to put the " valley " in the centre of the bed and brace B & C diagonally down to the legs, additional cross members at the leg / bracing joint would form a triangle.

The downside would be the 4th axis pat would be harder to reach being in the middle of the table. Another downside would be the " hole " in the top, I'm guessing if you went to the trouble and expense of a " valley " this might be of little concern, but would the spoilboard be stiff enough to bridge the gap?

I have wanted to build a 4th axis for some time but have only ever thought of smaller builds on top of the table. The idea of such a large capacity for an indexer is appealing.

Hope you are well.

Ed
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  #4  
Old Tue 22 September 2009, 23:15
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Hi Ed

Good to see you here again!

The center of the table takes the highest bending loads, so that is not a good place to start thinking of placing the valley.

However, a valley can be placed anywhere, provided that sufficient/correct reinforcing is put back in to compensate for the strength lost due to cutting a groove/valley in the table.

"would a better approach be to put the " valley " in the centre of the bed and brace B & C diagonally down to the legs, additional cross members at the leg / bracing joint would form a triangle"

We typically have 8 cross-supports and only 2 pairs of legs. But, yes, it would make sense to connect B&C to a lower longitudnal running between the legs. In fact, I would be tempted to make BC a full width cross-support and then raise the flat table surface up from that.......
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  #5  
Old Fri 20 August 2010, 16:02
Mountaincraft
Just call me: Mark
 
Shingletown, Ca.
United States of America
Forgive my significant ignorance.. but I'm not an engineer... what they heck are we looking at here? What exactly is an indexer? I'm not finding a mention of it in the plans or anything that looks like it.... But perhaps I'm looking in the wrong place...

Thoroughly confused,
Mark...
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  #6  
Old Fri 20 August 2010, 16:28
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
There is no indexer in the MM plans, although several people have added them. Think lathe. Replace the lathe motor with a stepper motor, mount the lathe so the gantry can pass over it, and you have a four-axis machine that can cut things like fluted spirals.

If you want to work with very large round thing, it helps to have a lowered area in the bed to place the indexer in - the "valley".
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  #7  
Old Fri 20 August 2010, 20:32
Mountaincraft
Just call me: Mark
 
Shingletown, Ca.
United States of America
Quote:
Originally Posted by bradm View Post
There is no indexer in the MM plans, although several people have added them. Think lathe. Replace the lathe motor with a stepper motor, mount the lathe so the gantry can pass over it, and you have a four-axis machine that can cut things like fluted spirals.

If you want to work with very large round thing, it helps to have a lowered area in the bed to place the indexer in - the "valley".
Hey, That's 'way' cool! So this is accomplished with a fourth axis motor/driver? Does the standard software that everyone generally use for their CNC routers handle this, or does it require a specialized program or plug in?

I was envisioning a fourth axis being used to carve in 3D by rotating the 'cutter' head around the work, but that seemed very unwieldy and complex... Don't know why I didn't think of rotating the stock instead, but that makes way more sense... This allows for true 3D work, with minimal complexity...

I have a poor mans version of such a thing out in the shop.. I think it's called a 'CraftMaster'... With it, a router is attached to a slide that moves along a piece of material that is rotated underneath it (spindle at each end) to create fluted spirals and what not.. It is completely mechanical in design, no robotics or automation of any kind, just cables and pulleys and screws...

With such a feature, the longer 14" Z slide option becomes much more valuable...

BTW, why is this feature called an 'indexer?'....


Thanks,
Mark

Last edited by Mountaincraft; Fri 20 August 2010 at 20:52..
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  #8  
Old Fri 20 August 2010, 21:48
KenC
Just call me: Ken
 
Klang
Malaysia
Mark, there are a few other factors to consider when looking/designing an indexer, eg, slender ratio of the work, i.e. when the jog gets long, it flex in the middle too much. When the diameter of the job gets bigger, dimensional resolution of the motor steps reduces.
So, big isn't always better...
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  #9  
Old Sat 21 August 2010, 13:54
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Index tradtionally can be found in the machinist world where a rotating device mechanically has holes and detents to accurately measure rotation for milling - In degree's, radians, mins, etc.

An indexer in the CNC world is "detented" by steps provided by the coded language via the Breakoutboard and Stepper driver.

I have built a very large scale indexer UNDER the bed of my MM #5. The indexer was capable of a 5' x 5' x 8' block of foam and the Z axis was modified for a 36" usable stroke.

Search under BBQ in the forum and you'll find it!

Sean
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  #10  
Old Wed 22 September 2010, 21:58
JamesJ
Just call me: Jim #104 (retired)
 
Kansas
United States of America
Forgive my ignorance but why does the indexer have to be mounted on the x axis?
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  #11  
Old Thu 23 September 2010, 00:07
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
It can be mounted on either the x or y axis. Usually the x axis is the longest and gives the capability of turning a longer workpiece. If you only need the smaller working size, many have mounted their indexers along the Y axis.
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  #12  
Old Thu 23 September 2010, 04:23
JamesJ
Just call me: Jim #104 (retired)
 
Kansas
United States of America
Heath
Thanks for the explanation. I thought it could be on either but was not sure.
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