PM 728 Comfort zone

T

Toro5xi

Registered
Registered
Joined
Apr 26, 2018
Messages
43
I’m flattening a piece of I think 1018 steel for a chuck mount. Taking a .030 depth of cut with a 3/8 4 flute carbon end mill. All axis locked except direction of travel and very little end mill stick out. 800 rpm I am feeding by hand until I feel machine vibrate and then try and slow down a little. Does this seem like a reasonable cut for a 728 mill?
I am struggling as I have no experience to know when I am pushing the mill to hard. I understand how many of you listen to the machine to determine when you are in the sweet spot. Could someone explain a little more how they determine that? Is a little vibration ok or have I already pushed it to far at that point.
Thanks for any input.
 
Last edited:
I would have to do the feeds and speeds calculations, but my gut tells me that 800 rpms is a bit slow.
Examine the condition of the cutting surfaces on your endmill, and make sure they are not chipped or rounded.
Are you using a coolant/lubricant with your cut?

I get 920 RPM, with a feed rate of 6 inches per minute, when using a carbon steel endmill.

A picture of the "chips" it is producing would tell us a lot.

Was your Endmill a "value priced" product? The cost/quality of an endmill can make a rather measurable difference. I have seen people think they had a problem with their milling machine, only to discover their endmill was the culprit.
 
Last edited:
Tom's Techniques (google it for the link) recommends a speed for steel using the simple formula:

RPM = 400 / diameter

The diameter is the size of the work if in a lathe, or the cutter diameter if using a mill. Using that formula, he'd recommend ~1100 RPM. Your 800 RPM's is close enough.

Your mill should handle that work with no issues assuming the steel is actually 1018 mild steel and the end mill is sharp. What do your chips look like? Smoking hot blue? Are you using any coolant? Brushing the chips away as you cut? Some photos may help.

Bruce
 
Thanks for the reply. The chips do not seem to have any blueish tint to them so I am guessing not absorbing any heat.
I will try a slightly higher RPM.
I purchased this end mill a few years ago but I tried to get a decent one.
I guess my question related to vibration is does that mean I am already getting chatter or is some vibration normal? I can understand speeds and feeds, math etc but just don't know how to get the feel of this without experience. I plan on looking for a tech school at some point.
It seems like many of you are able to push the machine until it pushes back. I know it is subjective but how do you know when that occurs? This was kind of a big investment for me. If I introduce vibration does that mean I am hurting the machine?
Thanks again for any input.
I am using a spray bottle of Mobilcut 100 10% solution. On occassion I did see some steam/smoke but very little.
The Y axis seems pretty snug gonna tweak the X axis gib a little.
 

Attachments

  • IMG_0454.jpg
    IMG_0454.jpg
    51.7 KB · Views: 122
How was the work piece secured to the table? If the piece has any ability to move (our bounce), it can give problems with finish and vibration. That groove in the picture looks very rough, how was it made? It looks like you were using the full width of the endmill for each pass.

The finish looks rather bad in the picture.
 
I made charts for my lathe, mill, and drill press with lines for each belt speed. Four columns for "largest diameter to cut" for carbide on steel, HSS on (steel, tough steel, Aluminum).

I also tried a visual chart with scaled circles on the lathe, but it just didnt sing to me :-(

Sent from my SM-G892A using Tapatalk
 
Btw, the chips look very dry even for HSS on steel. If you have an actual -carbon steel- end mill you really need to keep it cool. Carbon steel drill bits are barely ok-ish for -good-! High speed steel is really the minimum for any machine work.

Sent from my SM-G892A using Tapatalk
 
I was using at least a 90% step over. I will cut that back and use a little more lubricant.
The large groove in the middle is where I tig welded the two pieces together and just trying to flatten out the material. I used to work at a steel mill and have plenty of cut offs and drops to play around with.
Thanks for all the replies.
 
I would carefully check the cutting edges of your end mill. Different materials and hardness require different grinds on the tool. They also need to be sharp.
 
I ended up trying another carbide end mill and seemed like a better cut. Not sure the surface finish was any better but certainly less vibration.
Thanks for the suggestions.
 
You must log in or register to reply here.
Back
Top