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Need to make a big hole in Aluminum plate

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Investigator

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#1
I need some suggestions please, I need to 'bore' a 2-2.5" hole in 1.5" aluminum plate.

I'm working on a steady rest, my lathe didn't come with one. To that end I have acquired a piece of 1.5" aluminum (6061-t6 I think) which is 6x10", as well as some brass 'fingers' for the rest. I have pretty much worked out the steps I need to do everything but make the 'big hole'. I have a 12" Logan lathe and a RF30/31 mill to work with.

I think what I need to do is drill then bore it to size on a mill. Trouble is I have no boring head or tooling. Is there another way? Or do I need to bite the bullet and buy a boring head to do it?

Scott
 

David S

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#2
Let me be a bit crude, but could you drill a series of holes around the circumference of the hole and then cut out with a jig saw, and finish in the lathe?

David
 

benmychree

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#3
Get someone to water jet cut it, they could shape the whole works for you.
 

Dave Paine

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#4
The drill holes and use jig saw method of David S. could work, but you need to go slow with the jig saw. I tried using my jig saw on some 1/2in aluminium and within seconds the blade gullets were filled with cold weld particles. I had to pick these out one at a time then go much slower.

Another option is to grind a trepanning tool.

A Tom Lipton (Oxtool) video on this topic.

Tom Lipton video on trepanning tool
 

Investigator

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#5
I don't think turning the piece itself on the lathe is an option, at least not the way I am planning on making it. I could possibly make a tool on the lathe to cut the hole in the mill though.

The drill and jigsaw idea would likely work, but I'd rather do a more elegant and precise method if it's available.
 

benmychree

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#6
The drill holes and use jig saw method of David S. could work, but you need to go slow with the jig saw. I tried using my jig saw on some 1/2in aluminium and within seconds the blade gullets were filled with cold weld particles. I had to pick these out one at a time then go much slower.

Another option is to grind a trepanning tool.

A Tom Lipton (Oxtool) video on this topic.

Tom Lipton video on trepanning tool
One should always use a lubricant to avoid chip welding with aluminum; kerosene is the old standby but Magic Tap works well and is not so smelly.
 

GoceKU

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#7

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#8
Thinking off the wall here.....

I have a small rotary table. What about mounting it so that I could turn it under the mill head, and cut with an end mill?
 

DAT510

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#9
You could also use a hole saw, though the surface finish won't be the greatest. Drill/Hole Saw then boring would get you the nicest finish. If you get a boring head for your mill, as long as it doesn't have a fixed arbor, there are a variety of additional uses, such as a ball turner or as a means to further offset your tail stock, that you can use it for.
 

benmychree

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#10
That could work, (doing it on the rotary table) but likely you'd need to cut from both sides due to the thickness, same would go for trepanning. A hole saw is a option, also going at it from both sides.
 

DAT510

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#11
Thinking off the wall here.....

I have a small rotary table. What about mounting it so that I could turn it under the mill head, and cut with an end mill?
That would work..
 

Mitch Alsup

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#13
Thinking off the wall here.....

I have a small rotary table. What about mounting it so that I could turn it under the mill head, and cut with an end mill?
How small?

You are going to need clearance off the table so the end mill does not eat the table as the part turns around.
You are going to need a means to hold part to table while milling.

Other than that:: perfect.
 

MarkM

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#14
Locate your hole with your mill by drilling and then put a boring bar in a collett that will enable you to true up the hole. Either a fixed bar or use a bar that takes high speed. True the hole up then put it in your four jaw on the lathe and indicate the hole then your hole place is accurate. Now either bore the rest or use what you have to get close like a holesaw if you don t Have any big drills. I wouldn t trepan a hole that deep as everything has to be spot on when treppanning and the tool needs to be done well.
 

P. Waller

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#15
I have no idea what a RF 30/31 mill is but can you not interpolate such a small hole?

If not use a cheap fly cutter as a rough boring head after a hole saw or drill has made a starting hole, use a dial indicator to set the tool diameter.
This is slow and tedious but you only require one part correct?
 

pdentrem

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#16
These are 2 possible ways I would do this job. The Wire EDM machine would love this easy job but you have what you need to do the job.
I would use a 2 flute 3/8 or 1/2” end mill made for Aluminum. Rotary table with a 1/4” sacrificial piece of plywood or plastic cutting board. Bore your center hole which will be used to locate on center of rotary table. Use a 2 flute end mill and work down to pass half way, like about 1/4 to 1/2” from bottom. or cut through into that sacrificial plate.

Careful please read this part!
You do not want the center piece to break loose and trap the end mill as you approach the end of the cut. So with leaving 2 small retaining tabs about 180 degrees apart to hold the center plug in place. When done you should have a plug that is cut all the way except for two small areas that you can cut with a small saw and then blend into the rest of the cut.

Or flip before completely cutting through and avoid the sacrificial plate and cut down to about 1/4 to 1/2” left and flip, locate on the center hole again and continue to clear the remaining part but still leave the retaining tabs to hand cut at the end.
 

pdentrem

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#17
If the rotary is too small, Make an adapter that will allow the steady rest to mount to the rotary table. 1/2” Baltic plywood comes to mind as I have use this stuff for jigs and mounts quite a bit.
 

eserv

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#18
I'd do it with a holesaw as already mentioned. It'll be slow and you will need to clean out the chips often but you'll have a nice "slug" left to make something else out of! Best if you could do it horizontal.
 

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#19
A fly-cutter will work like a boring head, it's just harder to adjust. Here is a video of using one to cut a relief but it works for holes as well
Make the initial hole with a hole-saw.
 

jim18655

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#20
If you use a hole-saw try drilling 3 or 4 1/4" holes on the kerf of the saw. It gives the chips a place to fall through and out of the way.
 

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#23
................................

Careful please read this part!
You do not want the center piece to break loose and trap the end mill as you approach the end of the cut. So with leaving 2 small retaining tabs about 180 degrees apart to hold the center plug in place. When done you should have a plug that is cut all the way except for two small areas that you can cut with a small saw and then blend into the rest of the cut.

Or flip before completely cutting through and avoid the sacrificial plate and cut down to about 1/4 to 1/2” left and flip, locate on the center hole again and continue to clear the remaining part but still leave the retaining tabs to hand cut at the end.
Thank you! that is not something I would have thought of.
 

Jimsehr

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#24
When I made a steady out of alum I made the bottom of steady first . Then I put it on the machine with the hold down bolt snug. Then I drilled steady with a 1/2 drill in a collet by pushing alum into drill with tailstock. That way I knew 1/2 hole was on center of machine . Then I used that hole to center steady on rotary table. I worked from that hole to cut the 3 slots for the steady fingers. Then I cut the center plug out.
 

JimDawson

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#25
Thinking off the wall here.....

I have a small rotary table. What about mounting it so that I could turn it under the mill head, and cut with an end mill?
That's how I would do it given your available tooling.
 

tq60

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#26
Rent a hole saw from a rental place or buy one as they are handy to have.

Place wood under it clamped tight to table.

Slowest gear possible and peck drill.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

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#27
I was under the impression that a hole saw cutting that deep in aluminum was a problem. But that does look like the easiest solution. I have several hole saws already but hadn't really considered using one because as I said I thought it was somehow an issue.
I guess going slow and lots of cleaning out of chips would work and might be the easiest set up.
 

RandyM

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#28
Use a lubricant. I use WD40 for aluminum. You'll still have to clean the chips out of the cutting very often. I think the hole saw is really your best choice.

Another tip for this is to cut half way thru one side and then flip the part over using your pilot hole to line it all back up. This will keep the saw groove from getting so deep.

Good luck.
 

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#29
Another, albeit late thought. What would be the preferred size opening for a steady rest? Put another way, what size stock should I plan on being able to handle?

Talking this through in my head......My spindle is 1.375", so it seems there really is no value in making a steady for smaller than that since it could fit through the head stock and work close to the chuck. I guess making the steady large enough to handle a range from 1.375"-? would be a better plan.
So, 2.5"? 3"? does it matter how much of the fingers are extended past the rest?
Maybe the best design criteria would be what size hole saw I have readily available?
 

pontiac428

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#30
I cut a hole in 1.5 in aluminum plate with a hole saw... Once. Never again. I'd suggest hogging the hole out with a S&D bit then using a boring head or a fly cutting head in the Rong Fu. Rotary table would work well too.

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