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Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Rotary Table

The rotary table with an adapter plate and to this is mounted a Unimat 3 three-jaw chuck.

Small rotary tables such as 3" and 4" are ok, but unless you are machining very small parts it can be difficult to clamp parts down. A 6" rotary table is a better size and makes clamping parts down practical. Also, a 6" table will fit under most mini milling machines.


Used to machine:

  • arcs
  • flats on bolt heads and nuts
  • rotate a part to be drilled at precise divisions or angles
  • large circular parts that cannot be machined in a lathe

Division Plates

Fitting a rotary table with dividing plates turns it into a dividing head, the ratio of the worm-drive must be taken into account with the divisions of the plate.

Fixings

This shows a crankcase set up on the rotary table that is mounted to an adapter plate with a bolt through the centre.

The adapter plate is then bolted to the rotary table using T-nuts at the 3 points around the table.

This image clearly shows the bolt pointing upwards through the crankcase.

This is the crankcase for the poppet valve engine.


This milling process was done in two stages, this shows the first stage, the tool will then be lowered for the second stage.

You need to be very careful with cutting direction and be prepared to use the table locking screw as the table has a tendency to rotate with the cutter forces and the vibration.


Sometimes you get complacent.

I was in a hurry and thought for some reason that I could make a hardwood adapter.

What I just decided to ignore were the forces involved in end milling with a 12mm diameter bit and cutting speeds of around 1500rpm.

The cutter bit and jammed, nearly damaging the part beyond repair and nearly doing a lot more damage besides that.


This shows a close up of the adapter plate that was made from a piece of 8mm aluminium.

The bolts were recessed so that the cutter would clear them when machining the second stage that would complete the round body of the crankcase.

An 8mm bolt was fixed into the adapter plate and points up through the crankcase, a number of washers were then used and the part locked down with a nut. A dial gauge was then used to centre the part, rotating it back and forth whilst nudging it into location. The nut was then tightened and a second locking nut added.


A locking nut is important as the table was not large enough to get a fixing it that would stop the crankcase rotating with the milling forces. So the nut was tightened as far as possible and a lock-nut added to remove the possibility of it vibrating loose.

Machinging the small end of the master conrod for the 5 cylinder rotary engine with it held on the rotary table.

The Unimat 3 as a milling machine is just perfect for this type of work as it is very delicate and easy to set up.

Looking at this picture you can see just how wrong this is from a fixture stiffness and location viewpoint - however it worked.


The slot in the big end of the master conrod is for the slave conrods.

The rotary table is now in the vertical position.

The difficulty here was clamping the conrod tight enough with the bolt through the centre so that it did not rotate of it′s own accord.

If I had fixed the conrod directly to the rotary table I would have had an issue getting clearance between the chuck and the table.


Table Size

Rotary tables are normally specified based on the working table diameter. As with all things associated with the milling machine "larger and heavier" are always better.

A small 3" table is ok for use on a Unimat 3 milling machine and for very small parts. However, you will rapidly run out of room to get fixtures in place.

See also: Mill.


Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z