View Full Version : rotary tables
09-04-2001, 03:33 PM
What can anyone tell me about the 6,8,10" rotary tables like Grizzly sells. MSC and J&L also list them. $200-$400 approx. Would Put it on a Smithy 3in1 machine. Any ideas?
I don't know anything about those particular rotary tables, but I would encourage you to get the biggest one that's feasible. You need space to fit clamps and such, and the bigger the diameter the better. The table does have to be in proportion to your milling machine, of course, and it's also nice if you can install it without a crane, so don't just automatically get "the biggest one."
You may also want to look at horizontal/vertical models, which can somewhat take the place of a dividing head, especially if you can rig up a good way to mount a chuck on it.
09-04-2001, 07:19 PM
Thanks, SGW. I meant to say in my post that I was looking at horizontal/vertical units. Anyone else?
09-04-2001, 07:39 PM
I got a horiz/vert job from Enco. 6" dia fits nice on my Mill/drill table. Works good, no complaints, except I had to make some T-nuts for the little slots on the table. Probably coulda bought em, but didn't feel like waiting.
09-04-2001, 08:48 PM
I got one of what Enco calls the 'Super Spacers' a while back. 6" chuck, 8" face plate. It does everything I've asked of it.
I don't know the Smithy tool you mention. It is just barely a fit on the 7" x 30" knee mill I have.
09-04-2001, 10:27 PM
What's the difference between a rotary table and a super spacer?
09-04-2001, 10:38 PM
The Super Spacers have index plates for simple indexing.
A Rotary Table or Semi-Universal Dividing Head is worm drive and cannot do every division directly.
A Universal Dividing Head can do all divisions (even & odd) to the max # it is designed for
Super spcer vs. rotary table or index head:
The super spacers have a set of plates with holes in them, so you can index to whatever increment the hole spacing is. For a lot of work that's perfectly adequate. You need to index 2, 4, and 6 a whole lot more than you'll ever need to index 17 or 43, for instance.
An dividing head throws a worm drive into the equation (typically 40:1 ratio), so one turn of the crank gives you 1/40 a rotation. If you put, say, a 24-hole plate on that, moving one hole on the plate gives you 1/(40*24), or 1/960 division. You get a lot more combinations out of it. A dividing head oftentimes can pivot up/down, which gives more flexibility in the kinds of work it can handle.
A rotary table has a worm drive (typically 90:1) and a dial graduated in degrees and minutes (and seconds on really good ones). You can do any number of divisions you want; you just have to figure out the number of degrees, minutes, and seconds for each position. For say, 6 divisions, it's pretty easy: 60, 120, 180, 240, 300, 360. For 7 divisions...well, you work it out. :-) But it can be done, especially these days with a computer. You're limited by the accuracy to which you can set the dial, but for any normal work in a home shop it will be plenty close enough.
Sometimes index plates are available to fit on a rotary table, too; then it's about the same as a dividing head, although because the wormgear ratio is different the settings will be different.
[This message has been edited by SGW (edited 09-05-2001).]
[This message has been edited by SGW (edited 09-05-2001).]
09-05-2001, 05:23 PM
You can always put a larger top on a small rotary table, 6" table with a round 1 1/4" thick aluminum thats 12" in diameter, then put your own hold down holes where you want them.
09-05-2001, 08:21 PM
A note on the Super Spacer;
I don't know the ratio of the worm drive, but I have been able to use it as a rotary table, meaning I can start a cut at some specified radius from center and turn the work piece to get a large radius cut.
And, yes, it does have several plates to positively index at various degree specings.
09-19-2001, 07:09 PM
Buying a larger table is better, remember the table not only has to support the work but also has to hold the clamps. I have an 8 inch phase2(enco) table and have a large aluminum plate mounted on top to effectively provide a 16inch table. This works pretty well and is lighter and costs much less than a "real" 16inch rotary table would.
09-19-2001, 07:39 PM
Thanks for the information guys. I think I know what I need now. Not to clear on the ratio difference between rt and indexing plates but I guess I can figure it out when I see one
The ratio difference between a rotary table and an indexing head....
Nothing magic about it. A typical indexing head has a 40:1 wormgear in it and a typical rotary table has a 90:1 wormgear in it. That means, if you want to do 7 divisions, for example, you'll need to turn the crank of the indexing head 40/7, or 5 5/7 turns, or turn the crank of the rotary table 90/7, or 12 6/7 turns.
Therefore, on the indexing head you'll need a circle of holes on an index plate that is a multiple of 7 so you can do the 5/7 turn. If the rotary table has povision for indexing plates, you'll also need one with a circle of holes that is a multiple of 7 so you can do the 6/7 turn.
Or, more likely on the rotary table, you'd figure out that 1/7 turn is 51 degrees, 26 minutes (to the nearest minute), 2/7 is 102 degrees, 51 minutes, and so on, for all 7 divisions, and do the dividing by setting the degrees and minutes for each 1/7 rotation.
Does that clarify anything?
09-21-2001, 07:15 PM
Thanks SGW, that clears it up. Think I'll opt for the rotary table. Seems to be the most versatile. Don't know how accurately you can set the dials, but it's probably close enough.
09-22-2001, 03:43 AM
If the table you end up buying does not have division plates available you should consider a different one that does. Making new divison plates are not that difficult if you use the draftsman's "magic division strip". Of course, you could do the divisions with the "magic division strip" taped to the rotary table as well.
The whole point to a rotary table is to produce an accurately divided workpiece. You can do as SGW suggests, but adding all the degrees, minutes, seconds (*, ', ")up to index a prime number division (say, 67 teeth for a gear = 66 possible math errors) is going to drive you nuts. And, in all likely hood, ruin the work from from a simple error.
Even though I am a Medium-Crusty olde Fart with Bifocal disease I still get pissed when I make a boo-boo on something with a lot of work in it already.
Brown & Sharpe had a good point, K.I.S.S.
The division plates certainly make it easier, but with the computers and calcuators available these days it's not too horrendous to do the math for the divisions.
If you'd rather not do it though (and Thrud is right, it does take time, it is subject to error, and it's tedious), see http://www.jerry-howell.com/Gears.html
Jerry Howell has figured out tables of d/m/s for all divisions up to 100, and he's selling printed copies for $12.00. (Usual disclaimers.)
09-22-2001, 09:47 AM
I hate to be a pest but here is something else I don't understand. Where does the "maximum individual spacing error" come from? plus or minus 1'20" seems to show up a lot. Would seem that with a gear drive accuracy would be perfect as long as you keep backlash out of the picture.
I'm not sure exactly where you're getting the 1' 20" number from, but I assume it's because no gears are "perfect." There is some error in the worm and wormgear, and that may be the maximum allowable error for the class of gears that are being used in the rotary table you're looking at.
If you want to spend more money, you can get more accuracy. If you want to spend a LOT more money, you can get a lot more accuracy. Moore Special Tool Co. made (maybe they still do) a rotary table accurate to a few seconds, but the price would give you heart failure.
Let's see what 1' 20" really means. Take, say, a 10" diameter circle. Its circumference is therefore 31.415926535897..." , or let's say 31" for simplicity. 1' 20" is .0000617... of the total circumference (80 seconds divided by 360*60*60), or .0019" (31" times .0000617). So if you're dividing around a 10" diameter circle, the maximum error between two locations could conceivably be about .004" (if one was maximum + error and the next was maximum - error).
For smaller diameters the possible error will be proportionally less.
[This message has been edited by SGW (edited 09-22-2001).]
09-22-2001, 10:00 PM
SGW is right again. If you want a really good table Mecca, Nikken, Mews, and Yausa make beauties. You can turn a 3/4 ton load on the Nikken table while tilted - with your pinky...
www.gandmtools.co.uk (http://www.gandmtools.co.uk) -or- www.homeandworkshop.co.uk (http://www.homeandworkshop.co.uk)
had Precision Mecca 10" & 12" rotary tables with tailstocks, div plates and still crated 550 & 450 Pounds Sterling (repectively) freight extra.
Mecca claims 0*0'6" accuracy with the hand drum/vernier. I priced a 6 1/4" Mecca and it was $6000 Canadian.
09-23-2001, 02:33 AM
This is why I haunt this forum. I am new to machine work like this and am learning daily, I just added a great sum of knowledge.
Thanks for taking time to share.
09-23-2001, 07:50 AM
Thanks again for all the info guys. I wish I had machinery worthy of one of the real high quality tables, but I'm presently working with a small imported 3in1 machine. Think I'll stick with a smaller, less expensive table from MSC, Enco, Gizzly or someone like that. These tables are the ones that advertise the 1'20" accuracy that I mentioned.
For the stuff you're likely to do, one of the imports should work fine. You're probably not going to be working on things 10" in diameter, anyway. More likely closer to 2.5", so your maximum error at that diameter is about .001". And odds are it won't be that much.