cheap electric compound mitre saw vs. dedicated metal cutoff saw

Forgot to add:
    Most of the (power tool) work I do around the house involves carpentry.
Metal work is only for the robotics thing ...

Rotation speed is different, and woodworking tools lack coolant. In general,
light gauge non-ferrous sections and small bars should be OK. You need to
feed fast enough to minimize chatter and burning. The available power will
limit what you can cut. Steel and iron would be a bad idea even with
abrasive blades. The abrasive dust gets in the bearings and kills them
rather quickly.

I have a cheap Ryobi saw with an expansive aluminiun cutting blade in
it. I only cut Al and the results are good, once I got the setup square.
  If I was to buy another one I would make shure there was no tilt in
the direction when you are facing the saw.  It just makes it a hard to
get it square.

My setup although cheap it is more expensive than a really cheap chinese
metal cutoff saw.  But I think the large blade width on cutoff saws
would make it hard to work on more delicate/small parts.

I hate to reply to my own post, but just to clarify the blade I use is
nonabrasive.  It has smaller teeth than a wood blade.  I only cut 3-4mm
aluminiun and I have had no heat problems.  However it is quite noisy
but once aligned it very square.

Thanks for the info! The abrasive dust issue is something I never even
considered.

I also picked up an inexpensive set of standard thread taps at Sears. Again,
I will be working 90% of the time with aluminum. I noticed on the back of
the package it recommend using kerosone instead of cutting oil on aluminum.
Why is that ?

I cut a thread into an angle iron last night, which I think is steel (it was
pretty hard metal), and I just used some 3-in-1 brand oil instead of cutting
oil. Will 3-in-1oil work OK as cutting oil for the few times I will be doing
this ? Where can I get cutting oil ? ( I didn't ask at Sears because I
didn't think of it at the time).

Thanks for the help. This is of immense value to me.

In general, mineral oils -- kerosene is a mineral oil -- are recommended for
machining aluminum. I'm not sure of all the differences. Soluble oils are
more usually recommended for steel, so it can be mixed with water as a
coolant. For hand tapping, I can't see that it makes much of a difference. A
light film to hold chips in suspension is all you need.


Steel is about 3 times as dense as aluminum; the weight is a pretty good
indication which you have. Many aluminum alloys are as hard or harder than
steel, and equally strong or stronger. Steel is much less "bendy" and
changes size less with temperature. Broadly and generally speaking.

Marvel Mystery Oil (and 3-in-1) will work just fine. You just want some
lubricity, and to float the chips away.

Regarding tapping, don't forget to back up the tap periodically to break the
chip. About a quarter turn every half turn; you'll learn to tell by feel. I
think everyone has to break a tap for himself before taking this as
religion; practice on scrap until that happens, and then you'll be set.
You'd be surprised at the amount of words written on removing broken taps
and repairing the workpiece. (Come to think of it, the verbiage around
coolant selection eclipses even that.)

Aren't these really just kerosine, maybe desmelled a little?

Of course, all of the usual cutting oils are very flamable.
So be careful and keep the fire extinguisher handy


--
Pat

Yeah I did a good bit of tapping today. I was as surprised to see that the
oil did indeed help keep the filings "local" --- since I assumed it was just
for lubrication and cooling. Nothing like experience to see how things
really work !

Most of the metal cuts you might make with a mitre saw are much more
practical with a horizontal/vertical metal cutting bandsaw.  I use a cheap
($200 when I bought it) model to cut strips off aluminum plate up to 1"
thick, and to cut aluminum bars up to 4" thick.  You can cut iron, too -- it
just takes longer.  The advantages of the bandsaw are:

- The blade is cheaper than those abrasive things, and doesn't wear out
nearly as fast;

- Because the blade is thin, it removes much less material.  It takes a lot
less power, makes a lot less dust, and generates a lot less heat.

- You can use the horizontal configuration for cutting thick bars.  It takes
some time to cut a bar 4" thick.  You just set it and walk away.  It'll turn
off when the cut is done.

- It's relatively quiet.  Cutting metal with a circular saw is REALLY LOUD,
but I can use the bandsaw in the basement when my 2-year old is napping, and
it won't wake him up.

This is mine:
http://busybeetools.ca/cgi-bin/picture?&NETID"54181202050910345&NTITEM²442

In the US, you can get something similar at Harbour Freight.

--
Matt

Yeah I noticed that the abrasive blade on my circular saw is a LOT louder
than same saw cutting wood (normal blade)

I would assume a band saw might be more accurate, too ? So far I haven't
needed extreme accuracy, but I have noticed that I still need to file things
down to get them square like I want even using a t-square to guide the
circular saw.

For my current bot I should need to cut only one or maybe 2 more extrusions
to size, but if I need to keep doing so I will surely need to get something
better than what I have !

More accurate than a circular saw, but not as accurate as a mitre saw.  The
blade is flexible, so it's easy to push around. When you want something
really accurate, you'll have to cut it a wee bit oversize and grind it down.

 --
Matt

Hmmm ... that's good to know. I had the same result with trying a jig saw --
kept getting an angular cut everytime. Finally realized the blade was
bending as it traveled forward in the cut. Many things to learn, huh ?