PDA

View Full Version : cutting very deep keyway



TRX
05-26-2012, 06:11 PM
I have a print for a part that shows something like a semicircular Woodruff key slot. The with is .105" and radius is .940", but the depth is such that the shank on the cutter could be no more than .120".

The part was produced as a casting, but the prototypes were done on an ordinary Bridgeport-style mill. There's a small chance that this particular cut might have been done via EDM.

The print calls for a flat bottom and square corners.

The best I've thought up so far is to make a fixture to hold the part to the rotary table, turned up on its side, and rotate the part under an end mill, lowering the end mill for every pass. The floor of the groove would be curved, though. Not as much as a ball mill, and it would function properly, but it still wouldn't be per print.

Here's the relevant part of the blueprint:
http://i1267.photobucket.com/albums/jj558/TRX302/bolt3.jpg

With the depth of cut at .180", that's .060 max radius for the cutter shank, .120" diameter.

Anyone have any suggestions?

morehelium
05-26-2012, 06:39 PM
Whiskey Tango Foxtrot.

Man, someone needs a beating for drawing up something that gastly.

I don't have any woodruff standards handy but that seems wrong for a key slot.

First thing, is it something you are making for yourself or a job?

If it's for yourself analyze what the slot does and assess if it needs to be that deep or if a radiused bottom is ok.

If it really needs to be flat, cut it to depth with the method you proposed and grind the shank of a woodruff cutter to finish it off.

I'd make sure the woodruff cutter is narrower than the slot to minimize loading. In other words, do one side and move it over to finish the bottom.

The title suggests gun part, what's the hole near the bottom for?

Chris

TRX
05-26-2012, 07:00 PM
It's the bolt head for an antique gun. The keyslot is for the extractor. The blind horizontal hole on the bottom is for the ejection plunger.

I would do things differently if it was my design. Right now I'm trying to replicate the original as closely as possible.

jkruger
05-26-2012, 07:09 PM
A standard #304 cutter will do that very well if you grind the neck diameter down from .160 dia to .110. I think I have one already ground at work. The diameter of most keyseat cutters is smaller than the nominal. They say it is a 1/2" cutter but it is usually about .485 - .490. If not then just regrind the cutter to the right size.

TRX
05-26-2012, 08:00 PM
Yes, but that's a .500" diameter cutter. A .110" shank seems awfully small for a .940" cutter!

jkruger
05-26-2012, 08:11 PM
Yes, but that's a .500" diameter cutter. A .110" shank seems awfully small for a .940" cutter!

He wrote .940 but look at the drawing. It says .240R,+.005/-.000. That is .480 to .490 diameter. Methinks it was a typo Cap'n!

TRX
05-26-2012, 08:30 PM
.240 radius... .480 diameter. Arrrgh. I'm going to kick some dirt over that and pretend it didn't happen.

Is a .110-.120 shank really enough to do the job? Should I make a clean cut into the metal, or try to drill out as much as I can and use the cutter to clean it up?

jkruger
05-26-2012, 08:54 PM
.240 radius... .480 diameter. Arrrgh. I'm going to kick some dirt over that and pretend it didn't happen.

Is a .110-.120 shank really enough to do the job? Should I make a clean cut into the metal, or try to drill out as much as I can and use the cutter to clean it up?

I would rough it in with a unmodified #304 cutter and then finish with the one with the ground neck. Use lots of lube and go slow.:eek:

cameron
05-26-2012, 09:26 PM
If you do it on the rotary table, the depth of the arc across the bottom would be about 0.0006". With the tolerance of 0.005" on the radius, wouldn't that be good enough?

oldtiffie
05-26-2012, 09:32 PM
I've printed out the drawing and using the 0.420" dimension and a good office metric rule got the scaling factor I needed and applied it to the 0.240" wood-ruff slot radius and I got 0.238" which verified the scaling factor and the drawing dimension.

No matter how you grind the woodruff cutter shank as the base of the slot is circular at some point you are going to have the cutter trying to cut the whole curve in the slot no matter if a standard width cutter is used or even if multiple thinner cutters are used and when it has no lateral movement to "play with" it may well try to "climb mill".

The width of the slot is not given so I will asuume it is either 0.094" (3/32") or 0.125" (1/8") and as the cutter radius is 0.240" its diameter is 0.480".

The nearest cutter is either a #304 or 404 which are 3/32 x 1/2 and 1/8 x 1/2

The cutter nominal diameters are 1/2" so they may need to be ground back to 0.480" (2 x 0.240").

http://www.metalwebnews.com/formulas-tables/woodruf-key.html

(Note the cutting depths)

http://www.google.com.au/#hl=en&gs_nf=1&cp=19&gs_id=24&xhr=t&q=308+woodruff+cutter&pf=p&rlz=1W1IRFC_enAU360&sclient=psy-ab&oq=308+woodruff+cutter&aq=f&aqi=&aql=&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=696f04903ec9d5bc&biw=1280&bih=545

jkruger
05-26-2012, 09:51 PM
I've printed out the drawing and using the 0.420" dimension and a good office metric rule got the scaling factor I needed and applied it to the 0.240" wood-ruff slot radius and I got 0.238" which verified the scaling factor and the drawing dimension.

No matter how you grind the woodruff cutter shank as the base of the slot is circular at some point you are going to have the cutter trying to cut the whole curve in the slot no matter if a standard width cutter is used or even if multiple thinner cutters are used and when it has no lateral movement to "play with" it may well try to "climb mill".

The width of the slot is not given so I will asuume it is either 0.094" (3/32") or 0.125" (1/8") and as the cutter radius is 0.240" its diameter is 0.480".

The nearest cutter is either a #304 or 404 which are 3/32 x 1/2 and 1/8 x 1/2

The cutter nominal diameters are 1/2" so they may need to be ground back to 0.480" (2 x 0.240").

http://www.metalwebnews.com/formulas-tables/woodruf-key.html

(Note the cutting depths)

http://www.google.com.au/#hl=en&gs_nf=1&cp=19&gs_id=24&xhr=t&q=308+woodruff+cutter&pf=p&rlz=1W1IRFC_enAU360&sclient=psy-ab&oq=308+woodruff+cutter&aq=f&aqi=&aql=&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=696f04903ec9d5bc&biw=1280&bih=545

The #304 cutter is usually supplied at .490" or slightly smaller. The width is .093. One pass with a roughing cutter and then two with the undersized neck to finish the width and depth. These are very light cuts with the finish tool. This is not brain surgery.

lane
05-26-2012, 10:01 PM
I would use a woodruff cutter and just do it. Look at it this way some one else did it so why can`t you. They had the same tools as you .If not you need some more tools.

TRX
05-26-2012, 10:02 PM
If you do it on the rotary table, the depth of the arc across the bottom would be about 0.0006". With the tolerance of 0.005" on the radius, wouldn't that be good enough?

I expect it would.

I come up with these occasional stupid questions when I look at something and wonder if there's some process out there that I don't know that I don't know, if that makes any sense.

TRX
05-26-2012, 10:20 PM
Look at it this way some one else did it so why can`t you. They had the same tools as you .If not you need some more tools.

This print is of the production part, which was intended to be an investment casting with minimum machining. I don't know if the slot was machined or used as-cast.

Width is .105 +/.005, -.000

correction: examining the print again, it doesn't actually say it's a casting. Since most of the other pieces are castings, I may have made an unwarranted assumption there. This just hasn't been my day for blueprint reading...

jkruger
05-26-2012, 11:09 PM
I've printed out the drawing and using the 0.420" dimension and a good office metric rule got the scaling factor I needed and applied it to the 0.240" wood-ruff slot radius and I got 0.238" which verified the scaling factor and the drawing dimension.

No matter how you grind the woodruff cutter shank as the base of the slot is circular at some point you are going to have the cutter trying to cut the whole curve in the slot no matter if a standard width cutter is used or even if multiple thinner cutters are used and when it has no lateral movement to "play with" it may well try to "climb mill".

The width of the slot is not given so I will asuume it is either 0.094" (3/32") or 0.125" (1/8") and as the cutter radius is 0.240" its diameter is 0.480".

The nearest cutter is either a #304 or 404 which are 3/32 x 1/2 and 1/8 x 1/2

The cutter nominal diameters are 1/2" so they may need to be ground back to 0.480" (2 x 0.240").

http://www.metalwebnews.com/formulas-tables/woodruf-key.html

(Note the cutting depths)

http://www.google.com.au/#hl=en&gs_nf=1&cp=19&gs_id=24&xhr=t&q=308+woodruff+cutter&pf=p&rlz=1W1IRFC_enAU360&sclient=psy-ab&oq=308+woodruff+cutter&aq=f&aqi=&aql=&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=696f04903ec9d5bc&biw=1280&bih=545


I think if he roughs it in with the standard #304 cutter he will have only .005" or .006" per side to take out. If he goes to .235" in depth with the roughing cutter he will only have .005" to finish it to full depth. The reduced neck cutter can certainly do this and produce an excellent finish whether or not you consider it climb milling. There is no climb or conventional about it. It is a simple in and out cut with very little material removal.

oldtiffie
05-26-2012, 11:11 PM
I'd be interested to see how the woodruff cutter gets into the job if there is any obstruction to the collet or the collet holder.

Woodruff cutters are usually sized for making the cut in a cylinder - hence the shape of the "throat/neck".

The drawing gives no indication of what is either side of the key-way.

TRX
05-26-2012, 11:23 PM
That's an E-size (poster size) print; the part I posted was near enough to an edge I was able to use my 8-1/2x11" scanner on it.

The part is round, and there are no other cuts or holes intersecting the extractor groove. Well, there's a pivot pin hole, but it would get drilled later.

TRX
05-26-2012, 11:26 PM
I'll try a standard cutter and a reduced-neck cutter, then. Fortunately, I bought enough bar stock to experiment with.

Thanks guys!

oldtiffie
05-26-2012, 11:26 PM
All seems ready to go.

Best of luck.

strokersix
05-27-2012, 07:35 AM
You could do this with a single point. Swing the cutter by hand less than a revolution and you don't need relief on the opposite side. This way the cutter can be as rigid as required. And you don't need to buy any woodruff cutters. Just grind a bit yourself.

Uncle O
05-27-2012, 08:46 AM
I would like to suggest that perhaps the feature is over-engineered...

It would appear to me that the radius, and it's depth are all for clearance.
The width is more important, and pin (Axle) placement is more important.
If you go too shallow with the depth of the rad, you can buzz a little off the bottom of the extractor to gain the needed clearance to allow free rotation,
or movement.