Milling basics !

[JimM]

Hi guys

I’ve got my milling machine up and running and been having a play with it to get the feel of things. However I could now do with a few pointers on general machining principals and how to get the best from the machine

My first question is do with trimming stock to a given length

Eg I have 12 pieces of 1/2” square mild steel stock; they’re currently 1.125” long I need to trim them down to 1”. Is it best practice to lay the piece(s) down in the vice and remove the excess with the side of the cutter (ie table moves along the Y axis) or stand the stock up in the vice and use the end of the cutter (table moving along X axis)

Also how do I determine what size cutter to use or is it simply a case of bigger is better

Lastly I’ve found plenty of tables etc on cutting speeds, feed rates but not much on depth of cut – how do I determine what DOC to use.

I may be making things more complicated than I need to but if I don’t ask then I’ll never learn

Thanks

Jim

 

[b.lindsey]

Jim,
You will have more to grip on by laying them down in the vise. As far as the cutter size, as long as the flute length of the end mill is 1/2" or greater you should be fine. Bigger is better within reason...probably somewhere around a 1/2" end mill would be appropriate. Depending on the rigidity of your machine I would personally take it in 3 passes of say .050", .050" and .025" but you might sneak up on what works best in the first piece or two. Check the squareness of the vise if you haven't already, and use conventional milling (not climb milling) with the exception of retracing the final cut in the "climb" direction just to clean the surface up if needed.

Bill

 

[Babba]

You want the stock held as firmly & RIGIDLY as possible. In milling rigidity is everything, machine flex & tool flex are hard enough to dial into the equation without adding work piece float as well.

Not knowing what machine or vice your using I'd guess that you'd be better with the stock laying down rather than stood up.

Use the biggest cutter you can without going OTT, I'd be looking at using a 12mm (1/2") for your size stock.

With depth of cut (I only work with aluminium on my mill) I generally only go 1/3rd of the diameter of the tool as a maximum. Finishing cuts will be a lot less.

3yrs ago I was in exactly the same position, mill + tooling + stock + no idea. It's a steep learning curve & don't let anyone tell you it gets easier with time.

Keep reading, experimenting & above all keep asking, it's a lot cheaper than broken tools & ruined work pieces.

 

[Jasonb]

Probably faster to use a 4-jaw in the lathe

If I were milling them I would do it vertically, use parallels to set teh stock so just less than 1" is in the vice, use a milling cutter just larger than the 1/2" stock say 5/8 and if your mill is upto it .050, .050 + .025, less is both ends need machining from the saw.

Once you have checked the first one is on length you will just need to note the handwheel reading and can mill the rest down to length without measuring again,

Holding horizontal would need some form of end stop on your vice or measure each one and if it sa light mill using teh sibe of teh cutter may cause it to deflect.

Jason

 

[bearcar1]

I agree with Jason, if you have a lathe, the use of a collet and collet stop in the headstock and using a carriage stop, you could very quickly and accurately size the lot. Having to set each piece up in and out of a vice on the mill just seems too fiddly to me. Of course if one has to do it that way then that is OK as well but it will take a bit more time.

BC1
Jim

 

[kvom]

In the example given, I would mill them vertically as you can clamp most of the stock in the vise jaws. You will also get a better finish from the end flutes than the side flutes. Using the Y-axis will place the milling force against the jaws, which would be more rigid.

DOC and feed will depend on your mill. 1/3 of the endmill diameter is a good maximum. In the example case you need to remove 1/8", so that is not really a problem for a fullsize mill (e.g., BP or clone) with a 1/2" endmill. That said, with steel you will see the color of the chips; if you are getting blue chips then you might want to reduce the DOC or feed rate, or both.

Depending on how accurate you need the result to be, you probably don't want to take everything off with a single pass, esp. for the first piece. You can take a skim cut, measure the result, and then set the mill for the final length. Subsequent piece can be milled using the same setting in a single pass. If there are saw marks on both ends, you will want to true up one end first.

 

[joeby]

If you have a 6" vise, stand them all up in the vise at once, snug the vise and tap each one down to make sure it's seated. Use a c-clamp to hold them all together.

Disadvantage....cut one too short and they're all too short. Advantage.....if you are careful, you've made record time. I find I can make scrap much faster this way sometimes. :-\

Seriously though, I would rather take the chance on doing as many as possible in one setup because 1) my shop time is somewhat limited 2) I would rather not spend more time on an operation such as this than necessary (rather move on to the more challenging parts, I guess) 3) less chance of a narrow part wanting to roll-over in the vise 4) maybe less wear and tear on the tool (cutting the same amount of material; but less entering and exiting the cut) Probably more if I thought about it.

BTW, if you put multiple parts in the vise this way, put a piece of card stock or similar between the movable jaw and the work to take up any variation in size.

Just my $.02

Kevin

 

[Krown Kustoms]

I am a big fan of the fly cutter, stand them up clamp in vise, clamp both ends with a C clamp, take light passes, look at your smile in the reflection of the final cut.
If no fly cutter and you have to use a mill, use a .5in end mill and dont get in a hurry with the feed rate. If the flying chips burn your arms, you are cutting too deep.
just my 2¢
-B-

 

[rake60]

Jim
I would also recommend laying the stock flat down in the vise.
Clean up one end then crank it back to clean up the other end and measure
it. If the measurement reads .030" left, take .015" If all is perfect in the world
you'll have .015" left. Don't count on that happening!
Whatever is left take half of it again. Then trust that measurement to
adjust for the finish cut.

It's called "sneaking up" on a length or size.
Or,"operator finesse".

Machine tools are not perfect and metals are like a knotty pine log.
If you work that last cut to a minimum the machine will do it's best job
and an unseen hard knot in the material will not effect the outcome.

Rick

 

[Twmaster]

While I'm not a pro I would recommend you check out the Swarfrat.com videos. I've rented a bunch of them and bought their 'Vise Squad' DVD. Learned loads of good stuff.

 

[IanN]

Hi,

Another thing that will influence the best way to cut items like this is the type of cutter you have.

The type referred to as an "end mill" is designed to cut on its sides, not its end - it is for profiling rather than surfacing and can be identified by looking at the lips on the end of the cutter - they do not meet in the centre leaving a hole in the very centre. So if you have an end mill you should lay the blocks down and run the cutter sideways across the ends.

The alternative type of cutter, called a "slot drill", is designed to cut on its end. It can be plunged down into the work just like a conventional twist drill. The cutting lips on the end meet in the centre of the cutter. With this type of cutter you will get better results by placing the work o its ed and cutting with the end of the cutter running across the top of the blocks.

If you try to use the end of an end mill to surface, you will find the corners chip off of the cutting lips - to prevent this you should take the sharp corner off with a slip stone, it only needs a tiny chamfer but it prevents the cutter chipping.

Ian.

 

[woodchip85]

Centre cutting endmills are also available, they have the best attributes of both slot drills and end mills. The number of flutes can also affect finish and helix geometry dependent on the material your cutting, but that can become a little complicated.

 

[shred]

Btw, in the US, everything is an "end mill". Nobody uses the term "slot drill", yet overseas you'll get tsk-ed at for using "end mill" when you're supposed to say "slot drill". I think it's from the same people that came up with that little finger on the teacup thing ;D ;D

 

[GordTopps]

Hi Shred
It's not just a matter of ettiquette, there is a big difference between the two.
Check this link for a brief description/explanation.
http://machine-tools.netfirms.com/05_Types%20Of%20Milling%20Cutter.htm
Hope this helps, I'm no expert.
Gordon

 

[Artie]

Btw, in the US, everything is an "end mill". Nobody uses the term "slot drill", yet overseas you'll get tsk-ed at for using "end mill" when you're supposed to say "slot drill". I think it's from the same people that came up with that little finger on the teacup thing ;D ;D

tsk tsk indeed...'tire' 'aluminum' drop a 'z' in where an 's' should be...... tsk tsk indeed......


:big: :big: :big:

 

[joeby]

Just to stir the pot somewhat, a center-cutting end mill and a slot drill are one and the same. There are certainly non center-cutting end mills, but they are also end mills. So, and end mill can be either center-cutting or non-center cutting, a slot drill only center-cutting.

Center-cutting end mills (slot drills) are available in two, three, and four flute, but I haven't seen them with more than four flutes (doesn't mean they don't exist).

The differentiation comes from the fact that you cannot plunge cut with a non center-cutting end mill without drilling a start hole (not very easily anyway).

Kevin

 

[shred]

Hi Shred
It's not just a matter of ettiquette, there is a big difference between the two.
Check this link for a brief description/explanation.
http://machine-tools.netfirms.com/05_Types%20Of%20Milling%20Cutter.htm
Hope this helps, I'm no expert.
Gordon

We call what's listed on that site (a UK site) as a 'slot drill', "2-flute end mills" in the US. It's one of those Silver-Steel / Drill Rod; Rubber / Eraser things.


http://www.use-enco.com, a US tool supplier, for example has nothing listed under 'slot drill', but thousands of 'end mill's of all shapes and sizes..

 

[jwsvandr]

I don't have enough skills to comment with any authority but here is a collection of the best free videos I have come across on the web.

http://techtv.mit.edu/videos?page=1&q=Machine+Shop


If this doesnt work go to the home page and type in "Machine Shop" in the search box

 

[Peter Neill]

Just to stir the pot somewhat, a center-cutting end mill and a slot drill are one and the same.
Kevin

No they're not!
A slot drill is always a 2-flute cutter.

Peter

 

[Omnimill]

Thats what I thought. Until they started making 3 flute ones.

http://www.drill-service.co.uk/Tools.asp?Tool=100240000000

Vic.