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Old Brown and Sharpe Rotary Table Help Please

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Hi,
I was inspired recently to add a hold down or clamping fixture to my 10" Rotary Table.
The center hole is not a Morse Taper, just a hole.
In an effort to clamp a piece on the table, I would like to add an aluminum plate but I am not sure the best way to go about this.
Obviously to expedite table centering I would like to cut a standard taper of some sort to dial in center spindle on the Bridgeport Mill.
Based on this type of table, what would you do or what have you done to achieve my goals?
Thanks for the help.
Jeff IMG_1161[1].JPG IMG_1162[1].JPG
 

Comments

#2
I would just make a snug fitting plug to fit the RT hole, making sure it is tall enough to also index tight into the fixture plate. Hold the whole mess down to the RT with recessed SHCSs and t-nuts. Drill and tap the fixture plate as required to fit your jobs. This is assuming the round hole in the middle of the RT is precision placed, not just a rough hole.
 
#3
No, it's Brown and Sharpe precision. The table is very tight, It turns fairly smooth with no discernible lateral movement.
Using your idea, would you think chucking a 3/8 piece of tool steel in a 3/8 collet to extend and line up the bushing?
I could ream a 3/8 hole in the center of the bushing.
Am I on the right track?
 
#4
My other point, that I did not write, about using the table as is, is that putting in a Morse taper accurately concentric and square to the table top and bottom is not a trivial thing to do with typical home shop equipment. And, once it is wrong, it will be annoying from then on.

Yes, lining it up with a dowel pin or other known accurate locating pin would be fine, though it can move sideways and still go in the hole, so you still need to be careful when using it. A loose quill has slop when unlocked, and how accurately is the head trammed, how concentric is the collet to the spindle, etc., all matter, at least for fussy work. Also, the bushing you make will need to be accurately concentric and parallel.

Honestly, I use a very simple method for most work. My RT has a MT3 taper in the center. I have an extra drill arbor that fits the hole. I put an accurate rod with an accurate and coaxial 60 degree point on it in a collet, and then move the table around until the 60 degree point falls neatly into the center hole on the Jacobs taper end of the arbor. Done in short order. For fussier work, I use a Noga holder:
http://www.noga.com/Products/Centering/Centering Universal Holders/NF1018/Centering_NF_holder_3|fs|8"_-_NF1018
1537888862496.png
and a tenths indicator to center the hole to the spindle.
 
#5
Just turn up a plug with a center drilled in it. As Bob says, use a 60 degree point and locate from that. I do exactly the same as Bob !
Works for me...
 
#6
No, it's Brown and Sharpe precision. The table is very tight, It turns fairly smooth with no discernible lateral movement.
Using your idea, would you think chucking a 3/8 piece of tool steel in a 3/8 collet to extend and line up the bushing?
I could ream a 3/8 hole in the center of the bushing.
Am I on the right track?
I've got a 10" table with the same type of hole in the center I made a plug with a lip to go into the hole and put a dowel pin hole in the middle.

Stu
 
#7
I have a 12" RT with a 1" cylindrical hole in the center. I made a threaded plug to engage a 4" three jaw chuck from my 6 x 18 lathe. The plug has an internal 3/8-16 thread as well. On the back side of the RT, I mounted a close fitting plate which is threaded for 3/8-16. I screwed a stud from my clamping set into the plate and thread the chuck onto the stud. The chuck is now centered on the RT to the limits of runout on the chuck. It is easily removable if I need to clamp to the table.

My 6" Tormach 4th axis RT also has a cylindrical indexing hole at the center. The 5" three jaw chuck is mounted on a special backing plate which references the hole and is clamped to the table using the table tee slots.
 
#8
I've got a 10" table with the same type of hole in the center I made a plug with a lip to go into the hole and put a dowel pin hole in the middle.

Stu
Stu,
You use the dowel pin to line up the spindle? To center the table?
Bob, I agree with you. The morse Taper is not in my box of tools:)
I have a way or two forward now.
Thank you.
 
#9
Stu,
You use the dowel pin to line up the spindle? To center the table?
Bob, I agree with you. The morse Taper is not in my box of tools:)
I have a way or two forward now.
Thank you.
Dual purpose, I can use the dowel pin to align the table under the spindle and also use the hole to align the part (if it has a hole at the center of rotation).
 
#10
though it can move sideways and still go in the hole
Bob,
Could you please elaborate on your statement?
I can see some play due to lack of rigidity from the spindle and collet and length of the alignment pin to the table cavity.
 
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#11
What I did for my troyke 8” was turn a arbor between centers 3/4 on one side and turn a mt4 taper for the rotary.
Put arbor in machine then leaving rotary table loose align in taper and lock spindle. Then lock down rotary table. I use a 5” 3 jaw ontop the rotary usually but I put a pin in 3jaw. Indicate to your liking and tighten it down.
For a fixture plate just make the center hole a little oversized. Their is no real need for it to be precisely put on rotary table. Everything you mount to the plate will still need to be dialed in if you want it to be accurate.
Align the RT to the spindle lock the x and y. Mount your slab of metal to the table use the rotary to cut your OD. Then plan out your hold down hole pattern and go at it. If you put a sacrificial piece between the two you can cut the center hole too. Should be some good little projects. Good luck.
 
#12
Bob,
Could you please elaborate on your statement?
I can see some play due to lack of rigidity from the spindle and collet and length of the alignment pin to the table cavity.
Pushing a skinny, flexible cone into a fixed cone for an accurate fit has multiple problems. The shank flexes as the cones mesh, and it is difficult to see it happening. You have to inspect it critically to see what is going on. There are front to back and side to side issues, and you can only look from one viewpoint at a time. Bottom line, it looks like they are fitting together better than they really are. Same with a dowel pin, but perhaps to a lesser degree. A beefy accurate cylinder, with sharp square corners, dropping into a barely oversize hole, also with sharp square corners, would be the best way to do this kind of test, but then it would take some fooling around for a while to get it to actually drop into the hole...
 
#13
Not saying you don’t know what your looking at. But I would double check or confirm that the bore is not a Morse taper. Being a good quality RT I suspect it is a Morse taper hole. Take some ID measuring top of table,middle,and bottom. I thought mine was a straight bore till I dropped a #4 in the hole and it fit. Then I found the spec sheet on it and confirm it. Just a thought.
 
#14
Not saying you don’t know what your looking at. But I would double check or confirm that the bore is not a Morse taper. Being a good quality RT I suspect it is a Morse taper hole. Take some ID measuring top of table,middle,and bottom. I thought mine was a straight bore till I dropped a #4 in the hole and it fit. Then I found the spec sheet on it and confirm it. Just a thought.
OK, I'll say it, I have no idea what I am doing :).
I assumed it was a hole. I'll check for a taper.
It is still on the shelf. Dang these things are heavy.
Yep, it's a 1.250" hole all the way through.
I think for me, the 3/8 rod will get it close then I will indicate from there.
The spindle mounted Noga holder Bob showed us, IMG_1183[1].JPG is on it's way to my door step.
 
#15
I cut this center pin to a close fit. There are rough threads I could have used, but it is a locating pin, not a hold-down, so I didn't thread the plug. The bottom .750" of the table does have a MT for what it's good for. The pin constrains X and Y, the t-slots constrain Z.


(from mobile)
 
#16
Very helpful, thank you for posting.
 
#17
The bottom .750" of the table does have a MT for what it's good for.
(from mobile)
Yeah I would think any quality one would have it to use a center or drive bar. Do you know what size mt it is?
 
#18
Yeah I would think any quality one would have it to use a center or drive bar. Do you know what size mt it is?
On my little 6" table the center hole is a MT2. The table is a Kamakura Japan that I'd guess is 40-50 years old. Using it for a center or a drive hole is the the list of uses I could come up with for it in its entirety. With a lathe on hand, it's short work to turn any type of arbor one could need to accomplish an operation with the RT, which is pretty neat. It's an important capability for manual work on the mill. Edit: The hold down studs and hardware were under $20 from McMaster.
 
#19
Hi Guys.

26-09-2018-001.JPG
This is what I use to get my RT on center under the spindle.
26-09-2018-002.JPG
It is a 20 mm diameter, hardened steel pin.
 
#20
Boy, that is simple.
Great idea to get close quick.
 
#21
Hi Guys,

Yes I just stuff it into a collet and locate the table under it. It holds the RT whilst I move the mill table to fasten it down.
My RT is a six inch Vertex one.
 
#22
Mine is a 6" Chinesium RT with a MT center. I wanted a center hold down & made 1 to fit the MT center that bolts from the bottom, is just lower than the surface of the RT table & is threaded for a hold down. Why not make a plug, dial in center on the outboard of the RT table & then drill & tap a hole in the center of plug?
 
#23
Here’s a pretty easy expandable plug I made awhile back. Aluminum plug snug fit to hole then sliced and taper put in bottom. Stainless threaded taper gets pulled up into the plug and expands. Use any length bolt to hold your part down. That’s a 5/16-18 bolt for a size reference. Very useful for holding can be inserted in RT already mount and can be removed also without having to unbolt RT.
F708EA74-2746-4DF9-BC51-32C15B2E4464.jpeg 6700F533-3F55-4AE8-943D-EF3C6E767B5F.jpeg
 
#24
I just found a 1" thick piece of aluminum about 11" square.
I'll need to figure out a way to bore a center hole (Bridgeport) and mate it to the 1 1/4" RT pilot hole.
Should be a fun project. I assume once I mount the sacrificial plate, I can use a small rounded end mill and make the alignment rings.
This is uncharted waters for me.
 
#25
Real easy. Center your RT to the spindle on mill using your preference. Lock both axis. Then mount you aluminum plate on top a sacrificial piece so you can drill your center hole. Probably want to put your mounting holes for the plate in prior to this suggest a tapered head Allen so it will be flush or recessed from cutting surface. I’d fly cut plate then cut center hole making it as perfect as can be for aligning purposes. You can cut OD and put your alignment rings and fly cut all in one set up. Center hole should be a touch bigger than RT center hole so you can access without interference. A thing I’ve found is the slots in RT are never where I need them so a grid bolt pattern might be more useful for hold downs. Good luck.
 
#26
This is what happened to my 8” RT when I got it , mt3 center with a 3/8” dowel hole in it to center under spindle
025773DF-76D9-4E15-8F20-71DC88997C3B.jpeg
The plate is 1.250” mic6 drilled & taped for hold downs , the plug on the dowel centers the 4jaw or 3jaw
37CF9799-285A-443F-9355-CC3687349EFF.jpeg
A3816851-4888-4752-BFE0-A23A16AE7C44.jpeg 443A7FFB-578F-47AC-A845-7A6645D81B09.jpeg
 
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