I'm a newbie and just trying to learn to do machine work. I am trying to fabricate a special tool I need for working on my car. It's spanner wrench of sorts. Anyway, I need to cut a half circle with an 1 1/4" diameter into the side of some 1/8" plate. I was trying to do it with a boring head, but it doesn't seem to be the right tool for the job, or I am using it wrong. I am trying to do this on my milling machine, if possible. I was hoping someone could steer me in the right direction.
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- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] Cutting half circle in 1/8" plate
- Date: Sun, 3 Feb 2013 22:20:29 -0500
Cutting half circle in 1/8" plate
http://www.practicalmachinist.com/vb/general/cutting-half-circle-1-8-plate-259868/
Plastic
- Join Date
- Jun 2009
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- Oregon
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Cutting half circle in 1/8" plate
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02-03-2013, 05:54 AM #2
Hot Rolled
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- Jul 2005
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- UK
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Start with a piece of metal that is wider at the end where you want the semicircle to be .
Drill a 1 1/4" hole centered at the appropriate place .
Cut off the surplus metal
Job Done !
Davycrocket -
02-03-2013, 06:00 AM #3
Cast Iron
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I assume you are making a spanner wrench. If you do not have an endmill of that diameter, it can be tricky. I use hole saws to do this, but without the drill bit center. I have a 3 jaw scroll chuck mounted to an R8 adapter. I use that to hold the hole saw. If you don't have a quill chuck and have to use a hole saw normally, you must balance the saw and cut a complete hole.
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02-03-2013, 06:18 AM #4
Hot Rolled
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Why would that be a problem with a boring head ?
One of our younger guys in the museum team asked me if i could cut exactly that sort of half circle profile into the top of hot rolled c Channel so a Pipe could be welded into and the affair used as a housing for something.
Took a flycutter, put it in a Vee block and set the tool with a heigth gage for the required radius. Used the flycutter to scribe the half circle with the mill, a roughing endmill to remove 95% of the material and the flycutter to true it up.
Yeah, we currently dont have a boring head....sucks...big time....but it can be done even without. -
02-03-2013, 08:30 AM #5
Diamond
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Just to say perhaps the obvious, but if its just a clearance arc, you can draw it by hand and "mill by eye" to the line with something like a 1/4" EM. That doesn't teach you much about making beautifully dimensioned and surfaced parts but sometimes its more about getting the job done especially if your primary wheels are down for the count!
Files, oxyacetylene, plasma cutters, die grinder, or bandsaw blade could also replace the milling cutter.... -
02-03-2013, 08:53 AM #6
Diamond
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- Jan 2010
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The best advice is to purchase the tool, if the tool is available. Put it on a credit card, and while it's being shipped, do something productive.I was trying to do it with a boring head, but it doesn't seem to be the right tool for the job, or I am using it wrong
However....
You encountered a problem, what sort of problem?
What sort of mill? Yes, this website is a tough group, and if you respond "mill/drill" with a round column, the typical response will be "that's not a mill, it's not adequately rigid".
So.....what sort of problems are you experiencing? Can you post an image of the boring head set up?
You are attempting a trepanning operation, so let's take a look at the cutting edge.
You haven't declared the tools/tooling you have on-hand, so let's assume "not much".
Don't get hung-up on the following statements, unless they aren't true.
You don't have a rotary table.
You don't have a swivel vise.
You don't have a properly sized hole saw (which is okay, because hole saws are a poor excuse for whatever the proper tool would be).
You do have an endmill or two.
You have a clamping kit, or at least some pieces of a clamping kit. If you don't have at least one tee nut that fits the mill table, you really need to consider just buying the tool instead of creating it.
There are some details that work to your advantage. The arc is only 180 degrees, and the precision isn't too rigorous.
You could bolt the metal to a 2-3 foot length of board, perhaps a 2 by 4. Before you did that, you would create a pivot point on one end of the board, a counter-bored hole that would be a very snug fit for a hold-down stud/nut/washer. You may need to use a cheap bolt instead of the stud, to allow you to shorten it as needed, to keep it below the surface of the board, as needed. To get the needed fit, you may need to screw the bolt into that snug hole you created.
Get that set up on the mill, and verify it's all snug, but the leverage of the board allows you to spin it the required 180 degrees.
Use plenty of fasteners to clamp the workpiece to the board.
At this point, measure twice, perhaps three times. Maneuver the table to get the correct arc with the chosen end mill, and go about this using multiple passes, the first pass being very shallow, just to check the arc.
Or post photos of your boring head set up. -
02-03-2013, 09:57 AM #7
Plastic
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Use a hole saw as mentioned above, but how you get around the center drill part of it is you turn a shaft you can weld onto the hole saw and use the other end in a collet. Thus creating a endmill sort of. Just keep the quill lock on just slightly as you go down as to keep the "breaks" on. We use this method all the time for putting holes in things. If used gently these solid hole saws can last a long time and are great for coping of all kinds, before you know it you have collection of them! Just measure the id of the the hole saw threaded hole , turn a step on some 5/8 bar down to fit snuggly, use 5/8 collet for the shaft part of it, then grind paint off and weld. 3 small welds around is about all you need for small ones. Even if it wobbles a bit after welding, it works fine. We use these on 304 and 316 stainless all the time, so they are pretty tough. good luck!
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02-03-2013, 12:18 PM #8
Cast Iron
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good idea Defeatest, i use what i assume is a slitting saw arbor for hole saws here but it's a weird shop built one that i scored off CL with some other goodies and one off for sure. the other 'standard' stepped one i have doesnt fit the standard hole saw arbor hole.
works reasonably well but as SW Bausch said, it's not a very accurate hole size, i almost always chuck the boring head up after to cut to final size.
run thwe hole saw down to workpiece and just touch off, drill a small hole or two in the cut to release chips, go S-L-O-W! -
02-03-2013, 12:58 PM #9
Diamond
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Boring head should do this, no problem, but you have to understand that a boring head cannot cut the circle all at once. You need to start at the edge with the cutter very near the center and take out only .020 at a time or so, at most. That's going to take the better part of the day, especially if you don't have a boring/facing head with powerfeed so you don't have to stop the spindle every time you adjust the cut.
To plunge straight through with the boring head is called trepanning and requires a cutter with radial clearance on the outside so it doesn't drag in the cut. You'll also need a very rigid machine to get away with that.
Old school. Mark off your arc with a scribe, mark another line just a little less than 1/8" inside that one. Set up your drill press or mill with a 1/4" drill in the chuck. Drill a string of closely spaced holes centering on the inner line so the outside edge of the holes is almost touching the outer line (1 1/4). Chain drill this all the way around, then use a hack saw or band saw and cut the webs out from between the drilled holes. Mount back up with the boring head and clean it up to the line. If you want to go really old school, clean it up to the scribed line with a half round file. It'll probably go faster that way than setting up the boring head. -
02-03-2013, 04:44 PM #10
Stainless
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If the saw has a threaded arbor, and you're using a lathe to make a shaft to fit said saw, what the hell is the welder for?
Originally Posted by Defeatest
Face a 3/4 bar end, drill/tap it with appropriate threads (1/2-20 or 5/8-18), then use a bolt cutoff/set screw/all-thread/etc to screw the two together. -
02-03-2013, 06:34 PM #11
Aluminum
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Haugan rotabroach
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02-03-2013, 06:35 PM #12
Aluminum
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Jigsaw with metal cutting blade.
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02-03-2013, 06:44 PM #13
Aluminum
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- California, Ventura county
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rotary table and an end mill
if you have one of the new fancy DROs you can use the circle function.
Fly cutter -
02-03-2013, 06:50 PM #14
Cast Iron
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Mike's old school approach would be my mine as well, except that I would drill 3/16" diameter to reduce the mount of cleaning up, and done in less time than you'll spend messing around with getting mill tools, setting up and all that. It'll improve your skill and confidence with hand tools too. There is a very useful tension file called an Abrafile which was ideal for cutting the webs, but they are off the market now (unless you like paying stupid money for old ones on the internet). Originally Posted by Mike C.
George -
02-03-2013, 08:13 PM #15
Hot Rolled
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Your boring head would be a great tool to do the job with as long as you are holding the part correctly and useing the B head correctly.
Give it one more shot.
First,use a piece of scrap to set your diameter on the boring head.Take Bhead out and set it aside.
Next scribe a mark from the end of your spanner wrench to were you need the center of arc to be.
Then toeclamp your spanner wrench on top of a peice of flat material with the edges your are cutting into lined up down to your table.By putting something under your work you can hold it down and not have it jump around while cutting on it,the material underneath it is only to keep the work up off the table so you can make your cut and not get into mill table.
When you clamp the pieces down make sure they are square to either axis of the table...do not have to be dead nut,just close.
Now chuck something into your quill,like a small pointed tap of any size,then move over and alighn it over your mark on the work,zero dial or read out.If you have work alighned with X axis LOCK the table in X.
Now put your boring head back in the you have set to cut 1.250 diameter.Turn it on in the back gear of your mill running at about 200 RPM or so.Position it while running so that the cutterverly cuts on the edge of your work.
Zero dial or read out and move over .050" and make your cut useing the quills power feed.Keep stepping over .050 at a time till you have moved over exactly .625",now you are dead center of your ark to the edge of the work.
Make sure that both axis are set to zero now.
Remove boring head and put in your drill chuck,you can now do the math and move to the correct location to drill the pin holes. -
02-03-2013, 08:46 PM #16
Diamond
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George, I'll go you one better... I am lucky enough to own a Grob band file with an oval file band, lol. Zero effort.
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02-03-2013, 09:15 PM #17
Plastic
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- Jan 2013
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- usa
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- 6
Step 1 : stamping ( countour - hole - dia 1 1/4 - rectangular )
step 2 : drill 2 point- and press pin
Maybe you should welding . if so , it is stronger
tanphat206@gmail.com -
02-03-2013, 09:59 PM #18
Aluminum
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Re: Cutting half circle in 1/8" plate
I make my own hole saw arbours for use in the mill. Take a piece of cold rolled steel 1.5"dia x 3ish" long turn a shank to fit a collet, drill and tap the thread that matches the thread in your hole saw, should be 5/8nf for that size, all the way through the round. Now get a matching piece of grade 8 ready rod (all thread for you Americans i think) cut a piece that's about 1.5"longer than your arbour. Put flats on the top side and thread it all the way through leaving about a half inch sticking out the bottom. Screw your hole saw onto it and you have a very rigid hole saw. The flats are so you can loosen the hole saw once it's nicely jammed on there. I use this system for coping stainless tubing for the odd fab job i do:thumbdown:
Your using a mill so you don't need to screw around with a pilot. This will also let you cut nice discs out of plate.
Jordy Wallace
www.jorgometalworks.com
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- [machinist] Cutting half circle in 1/8" plate, Lawrence London, 02/03/2013
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