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dbasberg
01-01-2003, 03:56 PM
I am doing my first machining project (a model 109 steam engine from Tiny Power). It is a casting kit. I am to supply the 5/8" crankshaft with 1/8" keyway. I used 5/8" drill rod. I have broken 4 bits (1/8" end mills - 1 carbide & 3 M2 HSS). The drill rod was marked with light blue (baby blue) on the end. I believe it is water hardening. Do I have to anneal the rod before machining? I am using very slow power feed and 260 rpm. The depth of cut is 0.030". The chips make a very brittle sound while being removed, then the bit breaks. Do I change material for the crankshaft? Change the machining process? or take up knitting as a hobby?

------------------
Doug Basberg
Independent Engineering
Consultant

Big Dipper
01-01-2003, 05:31 PM
Try filing the drill rod. If it files fairly easy you shouldn't have a problem milling it. My guess is the sound you hear is the end mill grabbing/bouncing before it breaks. Without a CNC machine, you probably can't "power feed" slow enough for a 1/8" e.m. running at 260 rpm. Using HSS em's, I would suggest running around 1000 to 1200 rpm and about 2 ipm feed. End mills always "pull" to one side in slotting type cuts, especailly small ones. I like to rough keys out using a smaller e.m., then finish with a "size" e.m. Makes a better job of it.

Uncle Dunc
01-01-2003, 05:39 PM
What kind of bearings is the shaft going to run in? If it's just going in a hole drilled in cast iron, you might need the wear resistance of drill rod, but if it's going to have any kind of bronze or brass bushing, I think cold rolled steel would do fine. I agree with BD that any drill rod you can file can be machined without too much effort, but CRS is a little more forgiving.

I also agree with his recommendations about RPM and cutting undersize first.

Also, just occurred to me, are you using any lubricant? Nearly any lube at all is better than none.

x39
01-01-2003, 05:40 PM
Water hard shouldn't be any harder to machine than mild steel. You're breaking tooling because your turning WAY too slow. As Big Dipper suggested, speed that sucker up!

SGW
01-01-2003, 07:09 PM
I take it you're cutting the keyway.

Drill rod is no joy, no matter what you do with it, but you ought to be able to machine it in its as-supplied condition. Something like 1144 would be an easier-machining choice, though.

Figure 50 surface feet per minute is a pretty slow cutting rate. With a 1/8" dia. end mill, that works out to...1500 rpm, I think. 260 rpm is bog slow for an end mill that small. BD's 1000 to 1200 rpm ought to be a good conservative number. Ditto on the problem of end mills not cutting exactly to size when you "bury" them in something like a keyway cut. To have a better chance of getting an exact width, in line with where it's supposed to be, try an initial pass with a 3/32" end mill, then finish with 1/8". Oh -- a 2-flute end mill will work better for this than a 4-flute.

Slathering on some cutting oil won't hurt, either.

Feed rate is really difficult to judge with small end mills, because you can't feel anything. I try to go by seeing how fast the chips are coming off, and trying to keep it "reasonable," whatever that means. (If the end mill breaks, it wasn't "reasonable! http://bbs.homeshopmachinist.net//smile.gif )


[This message has been edited by SGW (edited 01-01-2003).]

Thrud
01-01-2003, 11:28 PM
Turn the speed all the way up. Chain drill the keyway with the end mill first if you still have problems then clean it out with a few slow passes - use coolant or lube. Two flute is best with the wee sizes and often all you can get below 1/8".

The other way it can be done is with a woodruff key cutter or a side cutting sliting saw.

SGW
01-02-2003, 07:01 AM
Yeah -- as per Thrud. A Woodruff cutter or slitting saw will work better, assuming you can live with a slighlty curved exit at the end of the keyway.

kap pullen
01-02-2003, 07:09 AM
Drill rod just costs you extra money, and causes you aggrivation.
Don't even think of welding the stuff.

There's no advantage to using tool steel if you're not gonna harden it.

Even your tool steel salesman will tell you this. Hell, I married my tool sales man.

That's the ONE thing she did tell me right.

If that's what you got, speed up the mill, or use a woodruf cutter as suggested.

kap

Al Messer
01-02-2003, 10:34 AM
What is this keyway for? If it's to hold the flywheel, consider drilling and tapping a hole in the "crack" and using a countersunk flat head screw to hold it together.

Oso
01-03-2003, 11:48 AM
I like Al's idea. Works well, seen it used on QC box shafts.

If you use a pin instead of a screw, you have some chance of replacing the shaft if you ever have to, though. The threads look about impossible to duplicate.

dbasberg
01-03-2003, 09:06 PM
<font face="Verdana, Arial" size="2">Originally posted by Big Dipper:
Try filing the drill rod. If it files fairly easy you shouldn't have a problem milling it.
&gt;&gt; Thanks, that test will be very useful...I'll keep it in my back pocket!

My guess is the sound you hear is the end mill grabbing/bouncing before it breaks.
&gt;&gt; Yes, that makes sense.

Without a CNC machine, you probably can't "power feed" slow enough for a 1/8" e.m. running at 260 rpm. Using HSS em's, I would suggest running around 1000 to 1200 rpm and about 2 ipm feed.
&gt;&gt; Novice mistake on my part...thinking slower speed is always easier on tool, but if speed is too low, then the small amount of material removed does not clear a path for the bit and the pressure builds up and breaks the tool...the weekend is here and I will try 1200 rpms and very slow feed (assuming the file says its soft enough...expect it will. Thanks very much.

End mills always "pull" to one side in slotting type cuts, especailly small ones.
&gt;&gt; Before the bits broke, the slot drifted off line...as you say. The smallest bit I have is 1/8 (I'll fix that soon) but for now, maybe a 3/16 keyway can be done starting with a 1/8 bit...thanks again.

I like to rough keys out using a smaller e.m., then finish with a "size" e.m. Makes a better job of it. </font>

dbasberg
01-03-2003, 09:13 PM
<font face="Verdana, Arial" size="2">Originally posted by Uncle Dunc:
What kind of bearings is the shaft going to run in? If it's just going in a hole drilled in cast iron, you might need the wear resistance of drill rod, but if it's going to have any kind of bronze or brass bushing, I think cold rolled steel would do fine. I agree with BD that any drill rod you can file can be machined without too much effort, but CRS is a little more forgiving.

I also agree with his recommendations about RPM and cutting undersize first.

Also, just occurred to me, are you using any lubricant? Nearly any lube at all is better than none.</font>

I tried a sulphurated oil used for tapping. The higher rpm will be tried this weekend...I expect that was my biggest problem. The shaft runs in a brass (or bronze) bushing(how do you tell the differnce between brass and bronze by sight?). I do not have 5/8 crs around...guess I could turn down some 3/4 stock.

Thanks for the good advice...it is most helpful.

dbasberg
01-03-2003, 09:15 PM
<font face="Verdana, Arial" size="2">Originally posted by x39:
Water hard shouldn't be any harder to machine than mild steel. You're breaking tooling because your turning WAY too slow. As Big Dipper suggested, speed that sucker up!</font>
&gt;&gt; Yes sir. I bet that will solve my problem...due to try it this weekend.

Thanks for the advice and letting me know that water hard is not hard to machine.

dbasberg
01-03-2003, 09:20 PM
This weekend I will put all this good advice to use. I do not have an end mill smaller than 1/8 to make a first cut for a 1/8 keyway, so I may do a 3/16 keyway starting with the 1/8 bit....Thanks for the help...it is much appreciated.


<font face="Verdana, Arial" size="2">Originally posted by SGW:
I take it you're cutting the keyway.

Drill rod is no joy, no matter what you do with it, but you ought to be able to machine it in its as-supplied condition. Something like 1144 would be an easier-machining choice, though.

Figure 50 surface feet per minute is a pretty slow cutting rate. With a 1/8" dia. end mill, that works out to...1500 rpm, I think. 260 rpm is bog slow for an end mill that small. BD's 1000 to 1200 rpm ought to be a good conservative number. Ditto on the problem of end mills not cutting exactly to size when you "bury" them in something like a keyway cut. To have a better chance of getting an exact width, in line with where it's supposed to be, try an initial pass with a 3/32" end mill, then finish with 1/8". Oh -- a 2-flute end mill will work better for this than a 4-flute.

Slathering on some cutting oil won't hurt, either.

Feed rate is really difficult to judge with small end mills, because you can't feel anything. I try to go by seeing how fast the chips are coming off, and trying to keep it "reasonable," whatever that means. (If the end mill breaks, it wasn't "reasonable! http://bbs.homeshopmachinist.net//smile.gif )


[This message has been edited by SGW (edited 01-01-2003).]</font>

dbasberg
01-03-2003, 09:31 PM
<font face="Verdana, Arial" size="2">Originally posted by kap pullen:
Drill rod just costs you extra money, and causes you aggrivation.
Don't even think of welding the stuff.

There's no advantage to using tool steel if you're not gonna harden it.

Even your tool steel salesman will tell you this. Hell, I married my tool sales man.

That's the ONE thing she did tell me right.

If that's what you got, speed up the mill, or use a woodruf cutter as suggested.

kap</font>
I do not have a woodruf cutter. I never heard of a machinist so crafty he marries for a discount on tools, so it must have been true love. 3 foot of 5/8 drill rod only costs $6.00, so my drive shaft is $2.00. I can handle that expense. I was thinking that hard/smooth surface would wear the bronze/brass bushing less...I sure could be wrong in my choice of material for the crankshaft of a steam engine. The plans I have did not specify a material and I had to guess what I should use. Several have advised to use CRS.
Thanks for your help and advise.

dbasberg
01-03-2003, 09:37 PM
<font face="Verdana, Arial" size="2">Originally posted by Oso:
I like Al's idea. Works well, seen it used on QC box shafts.

If you use a pin instead of a screw, you have some chance of replacing the shaft if you ever have to, though. The threads look about impossible to duplicate.</font>

I thank you and Al for these ideas on locking flywheels to crankshafts. I heard the designer of my steam engine later changed from the keyway/set screw arrangement with a taper pin locking method (similar to your suggestion). He suggested that the flywheels were working loose on the key and the taper pin worked better.

dbasberg
01-04-2003, 07:22 PM
I got some time in the shop today. The water hardening drill rod filed easily, so I cranked the mill up to 1600 rpm and did a 1/8 hss 2 flute mill by 0.025 deep and it cut like butter. The second cut was another 0.025 on slow power feed, again excellant! The third cut finished the total depth of .0635" that I wanted. The keyway mic'd to 0.1255" wide and was quite straight. I'm a happy guy. I intend to harden the area around the keyways for more resistance to damage. Now I am machining the crank disc from the cast iron casting. Then I will be broaching the keyway in that...we are on our way. This BBS is great. The great people who responded to help with my problem sure gave me good advise. I am very greatful.

Al Messer
01-04-2003, 08:26 PM
WARNING! THIS IS RANK HERESY!

You could "glue it together" with Loc-Tite. Even with 3/16" keyways in the axles of the drive wheels on my locomotive, I'm using Loc-Tite, but please, don't tell Thrud!!LOL

dbasberg
01-04-2003, 10:07 PM
<font face="Verdana, Arial" size="2">Originally posted by Al Messer:
WARNING! THIS IS RANK HERESY!

You could "glue it together" with Loc-Tite. Even with 3/16" keyways in the axles of the drive wheels on my locomotive, I'm using Loc-Tite, but please, don't tell Thrud!!LOL</font>

Loctite 609 goes into most press fit joints I make, but I had not thought of this application. Hmmm...sounds good
I was going to make a mandrel to press the crank disc on for turning the outside edge and that needed to be turned down from 3/4 stock. You have reminded me that a little 609 on a 5/8 shaft might be adequate for hold, then I can arbor press it off. What do you think? Is that a viable approach? (save a lot of chips)!

Thrud
01-05-2003, 02:36 AM
Al, Al, Al,
I ran out of firewood so we can't burn you at the stake this time. Actually it is a common trick in the UK.

Kap
A smart man marries a smart woman with her own tools - you is sneaky!