Making a fixture plate for a rotary table, hole pattern suggestion?

[WobblyHand]

Planning to make a fixture plate for my HV-6 rotary table. What is the most useful hole pattern? Square array? Polar? Something else? I am starting to draw it up.
For reference, I have a 6" table. An 8" plate will fit. Plate will be 3/4" thick aluminum. Will have a locating hole in the center. (Will machine an MT2 soft arbor.) Is there a hole pattern that you found useful, or no matter what one does, the holes are never in the right place! M8 mounting holes shown in picture below - match the tee-nuts I just made.

Should the tapped holes be blind?

 

[Cadillac]

I did a grid 1” on center through holes. Alternated rows on so it’s a diamond pattern. Works good does the job.

 

[jwmay]

I think the better plan is to put holes in it as you need them. Someday it'll have too many holes, and then you start over. But that may be because I'm too lazy to drill and tap a single hole I don't have to have.

 

[rabler]

I first measured both my mills plus my rotary table and designed a bolt down pattern that would work on the T-slot spacing on all three, in case I wanted to use it to hold something small on the mills. Then I added 3/8"-16 through holes on a 1" grid. Has worked well so far.

 

[rabler]

I would avoid blind holes in favor of all the way through, as I think blind holes would be harder to clean out chips after use.

 

[whitmore]

Blind holes are not useful, unless you think to protect the table under the plate? A simple sheet
metal subplate would do the same thing. The 1" grid, with 1/4-20 threads, seems a good plan;
if aluminum isn't strong enough, you can re-do later with helicoils, or insert some steel tee nuts
(AKA stepped threaded bushings) for press-fit from below.

I'd choose the 1/4-20 because that represents the biggest bucket of miscellaneous length
bolts in my collection...

 

[pontiac428]

Should you go with a 3-hole pattern, or a square pattern? I'd say both, for starters. That covers you for fixing parts with a radial 2-, 3-, 4-, 6-, 8- divided pattern. More versatile and better than having to make another plate for a quick job.

 

[WobblyHand]

Should you go with a 3-hole pattern, or a square pattern? I'd say both, for starters. That covers you for fixing parts with a radial 2-, 3-, 4-, 6-, 8- divided pattern. More versatile and better than having to make another plate for a quick job.

Everyone has given me food for thought. Right now this is my model for the plate. Beats me if holes are in the right places. It's a polar pattern. Holes are 1" separated in radius. 15 and 30 degree spacing. Kind of hard to get it to look ok and be functional. I do know that I will have to break the symmetry one day by drilling out a couple of new holes. At this point, I don't even know if I will drill all these holes! Thinking they will be M6, rather than 1/4-20 since nearly everything else on my machines are metric. Minimizes the need for double set of tools in the machine shop.

 

[compact8]

I am in the process of designing one for my RT. After some use, I found that fixing a fence that aligns with the Y / X axis at 0 degree is required in most cases and the fence has to be able to take up positions anywhere from close to the center of the table to some distance beyond the edge. That would suggest a rectangle plate with two rows of holes at the edge to fix the fence. I have something like this in my mind :



If you use parallels between the fence and the workpiece / vice then those two rows of holes will not be needed but still, the fence will need be outside the round table so that you can cut bigger radius. Other holes for clamping or fixing a small vice will be drilled on an as-needed basis. Some small clamps will need be made as well.

My very limited experience is that gluing the workpiece to the table solves a lot of clamping difficulties in many cases. To do so an additional aluminium sacrifice plate will need be mounted on top of the fixture plate and some mounting holes will be needed for that. After some use the sacrifice plate will have shallow grooves cut out here and there and will need to be re-flattened by milling.

 

[Lo-Fi]

I really like that rectangular plate idea. I use a fence on my RT all the time, it saves lots of setup time when used with adjustable parallels.