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Tips/Techniques Rotary Table fixture plates Ideas and experience

Tips/Techniques
Dabbler

Dabbler

ersatz engineer
In the dawn of time, I had a 6" RT. I had a job that I just couldn't clamp onto it, no matter what, so I built a 10"X10" fixture plate for it - it had 4 keys to tightly fit the "X" T-slots... It was made of 5/8 2024 aluminum, and it had custom holes drilled and threaded for the job. I had to round the corners, because they interfered with my column on that small mill, so I took perhaps an inch off of each one.

What characteristics would I choose for a 'topper plate' for a rotary table?
- I prefer square fixture plates for the extra clamping area in the corners, but it requires more clearance.
- Your overhang can't be too outrageous. The bigger the plate, the thicker it has to be.
- I like aluminum for the plate, noting it is getting expensive...
- Ideally, it would have a pattern of threaded holes and reamed holes like any other fixture plate.
- If it is big enough you can use your step blocks from your clamping kit.
- the perfect clamping arrangement is short clamps with a threaded hole at the non clamping end
(this is for a riser made from ready rod, so you can choose a custom size for the job)
- some guys prefer a locating hole in the centre. I locate the table before putting the plate on.

My perfect plate?

12"X12"X1" thick 6061 aluminum.
A 1" grid of threaded holes, except for the centre.
In the centre, a reamed 1/4" hole for a centre pin.
Interspersed with reamed 1/4" holes for locating pins.
Bolted in keys to locate the pate in the T slots.
 
I do more smaller part finicky work so my RT plate hole array is 8-32 based & a bit tighter spacing. That way I can use (smallest available) MiteeBite system for very low profile edge work. I also made custom clamps & arms & stop bars with slots to match. I find aluminum works fine for my needs. Steel/iron would be tougher especially on the threads, but weighs more. And depending on the alloy, watch for warpage. Square vs round has pros & con tradeoffs & personal preference. Some say if you can clear the extended corners of square, then why not make it round to that same footprint. Mine is round so I can also attach to lathe faceplate, particularly useful for off-center turning. But some guys take that a step further & use same fixture plate in a mill vise or clamped on mill table directly which may favor square/rectangular. Lots of useful possibilities.

Right or wrong, I selected a plate thickness where I could tap straight through. Its a pita job tapping all those holes even with a tapping head, but through tapping is generally easier than blind tapping. I guess that way you also have the other side to use if you bugger up one, but we never bugger things right? Just remember to accommodate other, typically different size fixture holes in your array so they don't intersect or otherwise look goofy.

Another material choice is MIC-6 or its equivalents. Its precision ground cast aluminum. There are places that sell offcuts. I was a bit worried about thread strength especially with repeated assembly & swarf getting in there but has been OK so far.
 
There is a CNC laser cutting shop near me; their off cut plates (4 X8 ft, and 5 X 9 ft) are placed outside beside the Aluminum recycle bin. At the time, they got around 1$ a pound, figuring in bin fees, etc. So we bought 4 sheets for 400$. From that, I managed several blocks in that size range. I mostly cruise for unwanted cutoffs at mid-sized machine shops, and usually get to score the odd good deal. I think we ended up at about 1.25$ a pound.

I usually offer about 75% of the current buy price for recycling. The current buy is $3.60.
 
I buy from a distributor and get wholesale rates, significantly lower because of the volume at each purchase. Additionally there are minimums that are involved. This order was about 600lbs of Aluminium, my biggest was about 1,400lbs.
 
i wasn't being cagey or portective I just forgot and was too lazy to look them up on Gmaps. They are Allied Metal. When I said when should I try again for another plate, the told me to wait "about 3 years"!
 
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