View Full Version : 4.5" radius in plate

09-05-2001, 12:30 PM
I have a 24" x 25" x 1" thick plate of 7075 Al. The botton of the plate has a 4.5" wide slot in the middle that goes 2/3rds up, terminating in a radius of, you guessed it, 4.5"

It looks like the below photo:


I am not really into making tool holders from scratch, so I was wondering what you guys recommend that can make a 4.5" hole and mill sidesways.

I do have a 2.5" new boring head with 3/4" tool holes that can make a 4.5" hole. Ever try to use a regular boring bar in a boring head and mill sidesways through something with sucessive depth cuts?

[This message has been edited by BigDave (edited 09-05-2001).]

09-05-2001, 05:18 PM
Rotary Table & A 3/4" end mill!!

09-05-2001, 08:14 PM
Hi, to the above I add a metal cutting bandsaw. Rough it (the slot) with the saw and then bore and finish. Looks like you used a rotary table for the holes so, use it in one setting for roughing and finishing the slot.
good luck

09-05-2001, 08:39 PM
I don't have a band saw, and the holes were put in on a CNC mill by the manufacturer.

I am doing it all on a 9 x 49 vertical mill. I will create coordinates for the hole pattern, so they won't have to be done on a rotary table. I probably ought to just slide out a HSS bit in a larger fly cutter and slowly take off a 1/16 in depth at a time....

The figure of a 4.5" rtadius was off by half, try 2.25" R for a slot 4.5" wide.

C. Tate
09-05-2001, 08:58 PM
Drill and bore your hole. Take an end mill and cut the sides out if you feed slow at the end of the cut you can let the center piece fall out. This will let you save the time of turning all of the aluminum to chips. If letting the chunk fall makes you nervous leave a small amount of material to hold it and use a jig saw with coarse teeth to cut it out, then finish with emill. Hougen makes a line of cutters that go in mag drills used on red iron work. These come in many sizes and use small amounts of horsepower. They have .750 shanks and work well in bridgeport style mills to make large holes. You can reharpen many times and hole size is very accurate.

I would stay away from fly cutters if at all possible, they are hell on spindle bearings in bridgeport style knee mills. I won't allow my people to use them on my machines. The large diameter cuts you are talking about can be made better with some of new indexable mills. They have inserts and cutters designed just for these mills that are very free cutting and require little horsepower. I even try and avoid these unless I have no other choice.

[This message has been edited by C. Tate (edited 09-05-2001).]

09-05-2001, 10:55 PM
You can get large diameter holesaws from Starrett, Greenlee, Lenox, or Ridgid all make holesaws - Plumbers and Electricians use them all the time for conduit & pipe. The hole can be sawn out and then finished with your boring head.

The slab sides could be roughed out with a Sawzall or portable jigsaw and finished with an endmill.

A water jet machine (CNC plate cutting) could also rought it out for you. The finish might even be usable as-is depending on application. (it leaves a "frosted" look on Aluminum)

Machining out the whole slot from the plate is a waste of time and the excess material should be sawn out.