Best way to cut 2.5" holes with non-CNC X3?

[Neil_J]

What's the best way to cut the following hole with a non-CNC Grizzly X3?

- Material: 6061-T6
- 2.5" diameter
- 1.5" deep
- Semi-circle "pillow block" (see picture below)
- Tolerance: +/- 0.05"
- Qty. 6

Do I need a boring head setup for this, or is there a quicker/easier way? I've never bored anything and actually I'm still a little confused on how I would actually use it and how long it would take to achieve a 2.5" hole.. For example, do I start with the largest hole I can drill (e.g. 1" dia.) and then incrementally bore 5 thou at a time until it's 2.5", or can you just start with the boring head at 2.5" and just start cutting? Also if a boring head is the way to go, would a 2" boring head cut a 2.5" hole, or would I need a 3"?


Life would certainly be a lot easier if I could do some circular pocketing but I'm months away from even starting the CNC conversion Anyway any help would be appreciated.

[Jason3]

Neil, how good does the surface of the bore need to be? If possible, I'd make 2 at a time, then cut it in half and clean up after boring with a boring bar, to avoid the interrupted cut. Drill it as big as you can first, then feed out 0.1' - 0.2" per pass until you're close, then creep up on final dimension (the bar will spring a bit)...

Regards,

Jason

[Neil_J]

Originally Posted by Jason3 Neil, how good does the surface of the bore need to be? If possible, I'd make 2 at a time, then cut it in half and clean up after boring with a boring bar, to avoid the interrupted cut. Drill it as big as you can first, then feed out 0.1' - 0.2" per pass until you're close, then creep up on final dimension (the bar will spring a bit)... Regards, Jason

The surface doesn't have to be precision at all. The pieces will be saddle blocks for a 2.5" diameter ultralight airplane boom. The flat part will go the L-channel that is part of the engine mount. So basically this pieces are square-to-round adapters See pictures below. I could probably do them with a hole saw if I was desperate enough.

One other idea I had was to use a rotary table with a milling bit, and basically cut the circles by cranking the handwheel. I could do like you said and cut them two at a time and at that point they would be a matched set.

So I could get a (cheap) 4" rotary table for $150-200 or a boring set for $80-100. They would probably take the same amount of time to machine, so it probably comes down to which one is more useful. I'm leaning towards the boring bar setup at this point.

[Teyber12]

hey!

a boring bar is a really handy thing to have. i bought one on ebay, a bridgport one (er- for a bridgeport ) which includes boring bar head, shank (r8), and a bunch of the actual boring bars for i think 90$ shipped.

I invested in some extra tooling a while ago (boring bar, hold-down set, more endmills, larger rotary table) and i can say the more tooling i seem to buy for my mill the more jobs i find being used on it.

Best of luck to you!

regards

[cncbasher]

by far the easiest way is to use a Fly cutter , this can be adjusted to cover just about any size you need , and is simple to use , just set it to the radius u need and gently plunge down , and gently move your table towards the cutter as you go taking slices as it were when you get near to size , you can adjust the dia of the cutter to get an exact fit to the boom , boring bars are fine but you would need to have a full circular hole to be cut which would be wasteful of material and in this case would take longer to acomplish .

iv'e cut semi circular holes using a fly cutter up to 5" dia without problems

[cncbasher]

Neil , here's a link for more info , which should explain

http://www.sherline.com/3052pg.htm

[jalessi]

YouTube - Flycutter

YouTube - Flycutter

[jalessi]

Using a rotary to bore large holes.

YouTube - 143: all setup to bore out the first block on the mill

YouTube - 143: all setup to bore out the first block on the mill

[cjdavis618]

While you could do it with the Fly cutter on your current part. You said that circular pockets would make life easier.

Get a rotary table, and call it a day. In the long run, you will be glad you did. Once you start your CNC conversion, you can then add a motor to it for 4th axis.

In fact, you might want to look at a dividing head. It will do the same as a Rotary table, but comes with a Lathe chuck plate. And will let you tilt from tilt from 0 to 90 degrees. If you really needed a faceplate to mount with, it would be easy to make. At some point, I am going to get one and convert it to CNC as my 4th axis. I already have the Grizzly rotary table and have it converted. No noticeable backlash and it is a very good product. But I want to expand my cutting angles beyond 90 and 0. I have a couple of cnc patterns that will require 45 degree drill routines in a circular pattern. So I want to add the Dividing head for that. (Yes I know I can tilt the SX3 head, but I would rather leave it trammed.)

Here is the dividing Head.

If you get a good rotary table that has indexing plates, or the Dividing head. You will be able to make perfectly patterned drill holes and a slew of other cuts that would be almost impossible without hours of math and notes.

Here is a youtube vid that shows a dividing head in use to make a gear.
http://www.youtube.com/watch?v=VHTXaU7GZC0

[ALLtra Mach]

I don't know what kind of boring bars you have, but it doesn't have to be a full circle cut. However it will be slow.
If the holes don't need to be precise, use an annular cutter and aas mentioned, cut two at once. You'll be well within your .05 tolerance and have all 6 done in half an hour.

[Neil_J]

Originally Posted by cncbasher by far the easiest way is to use a Fly cutter , this can be adjusted to cover just about any size you need , and is simple to use , just set it to the radius u need and gently plunge down , and gently move your table towards the cutter as you go taking slices as it were when you get near to size , you can adjust the dia of the cutter to get an exact fit to the boom , boring bars are fine but you would need to have a full circular hole to be cut which would be wasteful of material and in this case would take longer to acomplish . iv'e cut semi circular holes using a fly cutter up to 5" dia without problems

Well for me this is the cheapest way to go since I already have a flycutter. I'll try it out and report back here if I have any problems...

Thanks,

Neil

[digits]

How can you cut out a (semi-)circular pocket with a flycutter? It's the least centre-cutting tool I can think of - won't it just give you a shallow circular groove until it goes too deep and jams?