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Help Cutting square holes

focusrsh_b07732

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Dec 17, 2009
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I'm working on an Ansonia Gravity clock, remaking the rack and pinion gearing that powers the clock. However, this question is a general one.

There are two pinion gears that are peened onto an arbor that powers the clock. (See photo.) Two sides of the end of the arbor are flattened, and the hole in the gear correspondingly shaped, so the gear is locked to the arbor and can't turn. OK, making the squared end of the arbor is easy to do with a file or a mill. The questions is, how does one cut a square hole in a gear? (Or in this case, cut a hole with square sides and round ends?)

Are there square broaches for cutting square holes? And then would I need to use a VERY tiny file to round the ends? Or perhaps a very tiny endmill?

So the question is, in general, how to cut square holes?

pinion gear.JPG
 

bruce linde

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GregS

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1-dscn3329s.jpg

You don't always have to cut the hole square. When I needed to make a square hole for a gathering pallet I was making I ground this nail set square and tapered. Drilled a hole in the gathering pallet and pounded in the punch. turned it over and repeated on the other side. If I recall correctly it only took a 3 or 4 flips to produce a nice square forged hole.
Size your hole and punch to size of hole you need.
Greg
 

Willie X

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You can make a decent square broach from a steel chime rod. Just grind it to a long tapered square shape, on the side of a course grinding wheel. Leave it true but rough. Tap it in, not to tight, turn the piece over and tap it out. Repeat, repeat and repeat. If it doesn't need to be tapered, alternate from one side to the other. This works great with brass and OK with mild steel. Willie X
 
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Jerry Kieffer

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I'm working on an Ansonia Gravity clock, remaking the rack and pinion gearing that powers the clock. However, this question is a general one.

There are two pinion gears that are peened onto an arbor that powers the clock. (See photo.) Two sides of the end of the arbor are flattened, and the hole in the gear correspondingly shaped, so the gear is locked to the arbor and can't turn. OK, making the squared end of the arbor is easy to do with a file or a mill. The questions is, how does one cut a square hole in a gear? (Or in this case, cut a hole with square sides and round ends?)

Are there square broaches for cutting square holes? And then would I need to use a VERY tiny file to round the ends? Or perhaps a very tiny endmill?

So the question is, in general, how to cut square holes?

View attachment 576491

This is very easily done on a milling machine as follows.

(1) Drill a hole in the the new gear, same diameter as the width of the slot.

(2) mount the gear on the milling machine and position a endmill same diameter as the hole in the hole.

(3) Move the gear one direction then the other based on hand wheel settings to duplicate the original hole.

Setup photos on request.

Jerry Kieffer
 
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dad1891

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This is very easily done on a milling machine as follows.

(1) Drill a hole in the the new gear, same diameter as the width of the slot.

(2) mount the gear on the milling machine and position a endmill same diameter as the hole in the hole.

(3) Move the gear one direction then the other based on hand wheel settings to duplicate the original hole.

Setup photos on request.

Jerry Kieffer
I suspect that there may be some minor cleanup with a file because the diameter of the milled hole is equal to the width of the slot, which is smaller than the diameter of the arbor. However, it would be minor and would not affect the placement of the gear as long as you don't remove any metal in the center.
 

wow

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Jerry, could you please post photos of your set-up? I understand, but I don’t. How does the end mill cut the square corners?
 

Old Rivers

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I'm working on an Ansonia Gravity clock, remaking the rack and pinion gearing that powers the clock. However, this question is a general one.

There are two pinion gears that are peened onto an arbor that powers the clock. (See photo.) Two sides of the end of the arbor are flattened, and the hole in the gear correspondingly shaped, so the gear is locked to the arbor and can't turn. OK, making the squared end of the arbor is easy to do with a file or a mill. The questions is, how does one cut a square hole in a gear? (Or in this case, cut a hole with square sides and round ends?)

Are there square broaches for cutting square holes? And then would I need to use a VERY tiny file to round the ends? Or perhaps a very tiny endmill?

So the question is, in general, how to cut square holes?

View attachment 576491
Focus,

Not sure I am following...

One one hand you're asking "how to cut a square hole in a gear". This question I understand. But I am puzzled by your following parenthetic,
"Or in this case, cut a hole with square sides and round ends?"

Can you make a sketch which shows the shape of the hole you're trying to make?

Bill
 

focusrsh_b07732

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Dec 17, 2009
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I like the ideas by Greg and Willie to basically make a square tapered punch and drive it through the brass. Clever and cheap!
As for using a milling machine, well, yes, but that will require some pretty small end mills. Of course we are talking about clocks, so I suppose one is expected to have a selection of such miniature tools.
Thanks to all that responded.
 

Jerry Kieffer

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Jerry, could you please post photos of your set-up? I understand, but I don’t. How does the end mill cut the square corners?
First, to clarify, there are times when only broaches are practical.

The depth of a machined square hole is dependent on the length of the endmill used. Where practical, machining is is highly accurate and can assure that the hole is perfectly centered in the desired location.
The only disadvantage is that the corners have a slight radius often small enough that they are of no issue. However, slight touch up with a file or stone is a small price to pay for all of the other advantages once experienced.

In the OP`s photo, the ends of the slot are rounded and have no square corners as in the top attached sketch. (As questioned by Bill) Thus a endmill the same diameter as the width of the slot will duplicate what is shown in the OP`s photo.

When machining a new square hole or enlarging an existing square hole the process can be achieved as follows in the second attached sketch.

(1) Drill a hole the size of the square desired

(2) Mount in the milling machine in a chuck or collet on top of of a rotary table.

(3) Position the endmill at #1 and #2 and record hand wheel settings.

(4) Position endmill at #3 and move forward and backward stopping at recorded hand wheel settings.

(5) lift endmill (Z axis), rotate 90 degrees, lower the endmill and repeat the process above until the square has been completed.

One other advantage of machining when using a carbide endmill, is that you can often machine hardened/tempered parts such as hands.

The attached photo shows a 18s pocket watch square minute hand that could have been machined square or enlarged using the above procedure. The .015" 0r .375mm four flute endmills are shown for size reference and would have been used if such work were required. While difficult to see, the lower endmill is stub length and the upper standard length. For durability purposes, the cutting length of endmills should be no longer than required. Four flute have more material in them and are stronger with less chance of breakage where this may be a concern.

Also, the endmills shown will leave little more corner radius than the least sharp corner of the factory stock hand shown.

Jerry Kieffer

fullsizeoutput_531.jpeg fullsizeoutput_52f.jpeg
 
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wow

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Thank you, Jerry. I now understand. I must now purchase a variety of very small end mills. Mine are all too large for most of the small jobs I would be doing.
 

THTanner

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Jerry, could you please post photos of your set-up? I understand, but I don’t. How does the end mill cut the square corners?
I think he means parallel sides and rounded ends - so basically an oblong hole but the sides would be parallel. He describes a round arbor with two flat sides, so I think he is trying to get the fit tight over the two flat sides with rounded ends to fit over the rest of the arbor at that point?

A good drawing would help, but if there is enough space you could drill two hole a bit apart to make the rounded ends at the right distance, then file the flat sides in between?
 

bangster

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Take another look at that device in Bruce Linde's post.
 

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