Rotary table "lazy susan" style to compensate for limited y axis travel.

Hi All,
I recently took a job in the semiconductor industry as a design engineer. I've been machining my own designs for a few years on the puny machine in my garage. When they found out I could do CNC, my machine has been running a lot for smaller parts. We use a lot of in house fixtures for our process that are large (to me, too big for my machine). The parts are ~ 22" diameter 3"-4" thick made from 6061-T6. The parts are nothing complicated. Imagine a large Pie plate with pockets/tapped holes with a minimum wall thickness ~.25". They want me to bring the machining process in house due to our need for very fast turn around. Looks like my budget would be around $40K for.. I'm thinking of a used HAAS. These parts do not require any tolerances better than ~.008". From what I've seen these parts exceed the Y travel for machines in this price range. I've made large parts (plastic)similar on my mill by machining half/rotating 180 degrees,indicate, and finish the opposing half. Would it be possible to use a rotary table laid flat to simplify the machining of a part this large ?. would a Rotary table be rigid enough for aluminum used in this configuration ?.

Thanks in advance,
Matt

Possible, yes.

But think about the overhang on a 22" diameter 3" thick disc (X or Y; doesn't matter).

Rotaries, by design, have to have fairly closely spaced bearings, so the mechanical advantage is not in favour of that device.

So, it could work, but you may have to reduce rpm and feed to control chatter.

Going out on a small platter you are going to be reducing the rigidity a good amount. That said you can work around it somewhat.

My concern comes from the work envelope. Machines are encased all around with sheetmetal...so you can't overhang parts without them colliding with doors or the column. Also keep in mind when these machine startup, they need to go to a home position...the far right back corner. have to make sure your setup clears or it will need to be removed to home machine.

Haas shows layout online...call up the machine you want and layout your part...make sure it clears.

A 12" rotary table is a pretty good size, but even that would be lost under a part that is 22" diameter. You'd need to think of how you will clamp to the platter.

I'd think more about making a 'rotary subplate' than an actual rotary, something you'd index manually, with simple stop pins to do a 180° index.

On a Haas VF3, you can maybe squeeze 28" max diameter inside the enclosure with the door shut, and that is a machine with 20" Y travel, and 53" deep enclosure. You'd have to offset the subplate almost 4" towards the door (from the table center T slot) to get a piece that large in the machine. The max separation of the T slots in the table is only about 12.5", so the support and clamping options become limited when working way offset like that. I'd suggest careful modeling of your proposed machine table, its travel positions at extremes, and the part clamping to make sure what you can index will really work.

Yeah, I'm sure you could make a rotary work, but when you say your budget is 40k, I'm guesing the volumes aren't real high and you'd like to save some money. If it your own product couldn't you add a few holes in to use to locate it? Have a fixture plate, rotate the part manually, and reinsert locators. Shoulder bolts are quick, easy and cheap for this application. Use an undersize reamer to get a nice location fit on the shoulder bolts, and use some Delrin washers under the head of the bolt so you don't marr the part when you tighten the bolt.

And for the powerup issue with an oversize setup, you can just leave the machine on all the time. But if you don't plan ahead you could be a bit annoyed when you have a thunderstorm and the power blinks on ya.

Also I've seen a used VF-6's for under 40k, then you wouldn't need any special fixturing. 32" Y travel. Maybe you could even talk management into giving you bit more money for a VF-6 that isn't under 40k?

If you want to machine half a part index 180 degrees you don't need a rotary table. Put two reference holes in your part. Then either have a fixture plate with two pins to locate on or indicate the two holes after you turn the part around.

40k is a small budget might look at a Fadal 6030 as long as you don't need blinding speed
kind of like a tank it just lumbers along

Much as I'd like to have a machine with a larger Y travel, for those who are experienced, what is it like to load tools in a machine with more than 20" Y travel? A VF3 is comfortable to load (I'm about 6 feet tall), but to reach an extra 6" wouldn't do my back any good, and I have a good back.

Great info. Thanks everyone. I love this forum !. After looking into the rotary option and associated cost, think I'll just use a sub plate with locating holes and manually rotate the part.

If your tolerances are open enough, you may get away with using a CNC router instead. Bigger bed, plenty of travel for your part without indexing, and they usually go for less money than CNC mills.

We've done this before with rotary tables, but it's not a great idea when the part OD is twice the size of your rotary. What we often use in this situation is a air indexing "lazy susan" made of two main pieces. The part sits on the top plate. The bottom plate has an inlet for compressed air and a big groove in the face with an air outlet hole. The two are connected by a pin or bearing in the center so the top can rotate. When you turn the air on you can freely rotate the top plate, it's actually quite amazing at first how easy it is to spin hundreds of pounds with no effort. We use a locating block and dowel holes to index to the fixed locations so there is no risk of not hitting the correct angle after indexing. More work upfront than putting fixturing holes in your part, but it is very easy to use and can be done regardless of part geometry.

CNC hacker has the easiest/safest method.

Air-lift Rotary tables (Devlieg made tons of them back in the day), are fantastic for this type of work.

Something like this https://www.machinetools.com/en/for-sale/288807-giddings-and-lewis-air-lift-rotary-tables?q=Air+lift&btr=aHR0cHM6Ly93d3cubWFjaGluZXRvb2xzLmNvbS9lbi9zZWFyY2gvZm9yLXNhbGUvbWFjaGluZXM%2FY2F0ZWdvcnk9dXNlZCZxPUFpcitsaWZ0

Really quick to.

Wow, that's a cool way to do it, thanks