Looking for some basic info (Very New to Machining)

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colu41

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To start, I have Central Machinery Mini Mill. (Yes, Harbor Freight, but hey, it was partially a gift). I converted it to a belt drive to get rid of the plastic gears that break every 3 months but other than that she's stock.

I have a hobby of restoring high end putters for people and its getting quite busy! Any custom work like Welding or milling I send out to get done. Which is fine, it just adds time.

All I'm looking at doing is cutting small holes or "dots", and small lines into 303 stainless. Sounds simple, but I don't know if my mill is junk, or if I'm not running the bits at the proper speeds.

I did a practice run with 1/16 end mill. Ran it as fast as my machine goes (2500 rpm) and cut as slowly as I could, and it tore the teeth right off the coated carbide bit.

I can punch some dots decently fine, but still would love to know what speeds I should be using.

The size bits I'm using are:
1/16
1/8
3/8
1/2

Any tips would be great. I feel these are simple enough tasks that I can do it, just need suggestions to make the work as clean as possible. Thanks!
 
@colu41 ,

First welcome to the group!

I try to avoid 1/16" end mills. I swear they break by looking at them wrong.....

As with many things, this might not be as simple as you first think.
You specified the work-piece is 303 stainless and carbide cutter. Good.
There are many online charts for cutting speeds.
Cutter speed, diameter and material is certainly a part of it, but there's more to understand.

We need more info, things like:
-what kind of cut? (some end-mills will plunge cut, some won't)
-what kind of tool? (you said carbide, I assume end-mills, are they ball-end or square end?)
-for the "lines" are you using an engraving bit, or the corner of an end-mill?
-what is the depth of cut?
-what is the feed? (how fast is the work pushed into the rotating tool?)
-how is the work being held? in a vise?
-are the table gibs adjusted? are you locking the axis you're not moving?
(any "flex" in the holding system can lead to chatter and worse)

I am NOT trying to scare you off!
Just give us as much info as you can and there will be a wealth of responses and recommendations.
Pictures would help!

Brian
 
Thank you!

I sort of assumed it wasn't going to be as simple as I originally thought. When this mill was brand new I felt it worked very well. Then everything sort of got "out of tune". And years back I've messed with the gibs a bit but never really understood how they are properly adjusted. So I'll go through your questions.

Cut: I guess I'm looking for just a plunge cut. Just a straight down into the steel cut about 1/16 or less deep.
Tool: They are square end TaIN coated carbide end mills
The lines: Using also a square end mill
Depth: Again no more the 1/16. Even less.
For speed: I feel like I was turning it by hand as slowly as I could?
Work is held in a mounted vice.
Gibs MAY be out of adjustment. When i did a very shallow cut with the 1/2" end mill it did chatter a bit.

I guess we can start with how to properly adjust the gibs, and if I even have the correct bits for the job?
 
Yes I was keeping the feed as steady as possible. When cutting just a straight hole, it completely flew my mind to lock both axis. So I did another cut and seemed a lot smoother this time. Still won't be attempting to mill a slot/line until I figure out if/when my gibs need adjusting.
 
The fact that locking the gibs when plunging helped is telling.
That might be your main issue.
I don't know that machine; others here can guide on gib adjustment.
Do you have a manual?

One other thing I just thought of is mill tram. That is if the spindle is exactly 90 degrees to the table x and y movements.
If it is out of adjustment then you can get extra chatter and "scallops" when cutting grooves.

Stay with us, we can help figure it out.

By the way, I was looking for a reference for center-cutting vs. non-center cutting end mills. This is the best picture I have found:
1683113203978.png
from here:
https://f.hubspotusercontent00.net/...ides And Downloadable PDFs/End_Mill_Guide.pdf

Weird that there were so many un-useful or just plain wrong references.... but I guess I shouldn't be surprised on the internet....

Brian
 
Thank you! I got this mill probably 7 years ago, and moved homes since so, no manual. But could easily look it up. Definitely need to make some adjustments. I believe I have the tools to tram it properly also. Just dug out the magnetic dial so will have to see if I remember how to use it.
Also, I do believe my end mills are the NON center cutting :(
 
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