Broken Bolton BT-800

Hmm. It says that I do not have permission to view the page when clicking on those links. Anyway, google led me to this calculator ... I chose Alloy Steel (not sure what trailer hitches are made of!), left the cutting speed at 90 fpm (still not quite sure I understand fpm in this context) a .250" HSS bit with 4 cutting edges, and entered the machine's max speed of 3000 rpm. It came up with 1380 rpm, a feed rate of 7 ipm (3 ipm for 2 cutting edges), yielding a "chip load" of 0.0013 in/flute. Does this all seem correct to you? Much of this confuses me. How deep should I go when making a rough cut?

Anyway, I tightened the spanner nut down to where I could feel the bearing starting to get tight, and backed it off just a little bit, perhaps 1/16 of a turn and tapped it down so it feels very free when spinning it by hand. I cannot feel any up and down movement when pulling up and down on the shaft. I am not sure how this is supposed to feel ...
 
aPpYe said:
Hmm. It says that I do not have permission to view the page when clicking on those links.
Click to expand...

Whoops, there may be a donation requirement for access to downloads.....sorry I did not mean to tease you.
I went looking for a link to the rules for the downloads section and did NOT find it......I will post back if I do.

I have used that Little Machine Shop calculator too.

aPpYe said:
left the cutting speed at 90 fpm (still not quite sure I understand fpm in this context)
Click to expand...

Yeah, that can be strange to get your head around at first. I believe the terminology really comes from lathe work, where the RPM of the work piece and the work piece diameter together determine how fast the outer surface of the work is coming past the tool bit. (Actually it's the work piece circumference that matters, but that can be calculated from the diameter, or radius; C = 2 * pi * r = pi * d)

However, since the exact same math applies to a milling machine where you spin the tool (an end-mill), the same terminology is used.
The only caveat is accounting for the multiple cutting edges of the end-mill vs. the single edge of the lathe tool bit.

Another handy speed/feed calculator resource is the Niagra Cutter Speed/Feed slide rule that you can get for free:
http://niagaracutter.com/speed-feed-slide
Someone here had posted that link years ago....I was doubtful, but they did send one to me in Canada.
My thanks to whoever originally posted it.

For 90 fpm, and 1/4" end mill my slide rule shows about 1375 rpm.
Then for a 7 ipm feed rate that gives about 0.0013 chip load.

aPpYe said:
Does this all seem correct to you?
Click to expand...

So yes my slide rule agrees with the LMS online calculator.

-brino
 
So what about depth? Meaning, how much can I mill off at one time? Does the same calculation apply whether I am milling .250" or .005" off of a surface? I ask because I have nearly .250" to mill off of one piece to get it to equal the first one.
 
Sorry @aPpYe , I was hoping someone else would jump in with experience in this......

Depth of cut depends on many things; material type, cutter type, speed, feed, machine rigidity, etc.

I never use math to calculate a depth of cut......I kinda wing it....based on experience.
I start smallish and work up until it doesn't sound/feel right, then back it off a bit.

-brino
 
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