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View Full Version : Were helical milling cutters ("slab mills") ever made in carbide?



Arthur.Marks
09-16-2014, 11:32 PM
If they were, it must have been in very small numbers. Everything else transitioned into brazed carbide, solid carbide or inserts. Why not arbor-mounted, plain, helical milling cutters (http://www.victornet.com/alphabetic/Milling-Cutters-Plain/643.html)? Just curious, really :)

oldtiffie
09-16-2014, 11:42 PM
https://www.google.com.au/?gws_rd=ssl#q=carbide+end+mill

PixMan
09-17-2014, 07:46 AM
Yes, and they still are made. Not many are sold because the machines which run them are generally to slow in RPM and too weak in HP to take advantage of the carbide. There aren't as many slab mills as there are larger diameter slotting cutters.

More importantly, the HSS slab mills and the machines which run them are usually built for conventional milling. Carbide insert cutters are best used with climb milling. Try that on an old Acme screw Kearney & Trecker or a hydraulic Cincinnati and you'll have yourself a major mess of broken tools, spoiled work and bent arbors.

wierdscience
09-17-2014, 09:03 AM
I've seen plenty that had brazed carbide tips,usually a low flute count(5-12 depending on diameter).

Most common application was machining cast Aluminum or Iron where abrasion is a problem in production.

Never have seen one in solid carbide,I would hate to think what a solid carbide slab mill in say a 4" diameter x 6" width would cost $$$$:eek:

Old Hat
09-17-2014, 10:38 AM
Slab milling is / was an "over-arm only" adventure.
About about as much latteral cutting force as you're ever going to develope.
Very slow spindle speeds, and the rolling action of the flut edges
would rapidly destroy a cutter of that geometry made from carbide.

The whole reasoning behind appl~ing carbide to cutting metal,
and the constraints and advantages of carbide use, are a missmatch
to the method of slab-milling.

For about a decade now, and for good reason, "High-Feed" milling
is all the rage. Spindles have to be extremely well built, and you'll
use allotta horsepower....... BUT no more cutting forces in the thousands of pounds.
Tool-slides and ball-screws have a much nicer time of it now.

And with most alloys, the chip-shape is easilly handled by chip-conveyors,
not to mention most "High-Feed" cutters are best off run dry or with airblast.
Tungaloy makes a line of tuff High Feed inserts that can go wet,
for you wet-working enthusiasts.

TGTool
09-17-2014, 11:05 AM
If HSS was ever at the limit of it's capabilities in the old days the next step up would probably have been stellite tips. Stellite could have been welded on and ground to shape - no trivial exercise - and the cutter would hold up beyond HSS.

A friend of mine (god rest him) thought home shop machinists might really prefer stellite over carbide since it will hold an edge better and doesn't need the feedrate that carbide does to cut effectively.

Old Hat
09-17-2014, 11:14 AM
If HSS was ever at the limit of it's capabilities in the old days the next step up would probably have been stellite tips. Stellite could have been welded on and ground to shape - no trivial exercise - and the cutter would hold up beyond HSS.

A friend of mine (god rest him) thought home shop machinists might really prefer stellite over carbide since it will hold an edge better and doesn't need the feedrate that carbide does to cut effectively.

+1
Some lot offerings on Ebay have stellite mixed in,
but unless pic quallity is high it's hard to find it.

I'm a fool for doing this, but since I don't have a lathe at home.
http://www.ebay.com/itm/2-Super-Alloy-525-Thread-Cutter-3-8-Lathe-Tool-Bit-Machinist-Gunsmith-Sherline-/261592137613?pt=LH_DefaultDomain_0&hash=item3ce81b3f8d

Arthur.Marks
09-17-2014, 02:13 PM
Very slow spindle speeds, and the rolling action of the flut edges
would rapidly destroy a cutter of that geometry made from carbide.

The whole reasoning behind appl~ing carbide to cutting metal,
and the constraints and advantages of carbide use, are a missmatch
to the method of slab-milling..
I don't think I follow. End mills have a very similar helix, although a selection of helix angles is typical for slab mills. And cutting speed is a function of work material, tool material, and proper SFM. In that respect, there is no difference. Just because a cutting diameter is large and looks relatively slow moving doesn't, of course, mean the actual SFM is in any way low. The SFM for carbide would raise the spindle speed significantly in comparison to a HSS slab mill.

As mentioned, cost would make one shudder for a solid carbide slab mill. That makes sense. I guess brazed carbide edges would have an impracticality about it due to the single, continuous, curving cutting edge. I hadn't really considered that... Producing the shape necessary to braze an edge on would have to be complicated. This fact is reinforced by the common availability of slotting cutters with brazed tips. Those have a simple square piece of carbide brazed on and sharpened into shape. So possibly cost plays/ed a significant role in comparison to other options available.

Valid point on the climb milling aspect, but it seems that most tool materials benefit in finish and longevity by climb milling if it can be rigidly accomodated by the machine. That said, it doesn't often mean conventional cuts can't be used with the same tools. Besides, anti-backlash mechanisms have been around for at least half a century---well back into the manual machining era.

J Tiers
09-17-2014, 08:25 PM
I've seen pics of the insert type, but not one up close.

Interestingly, I do not find slab milling to be a high pressure /force operation. I rarely take off more than 0.125" at a pass, because I do have a small mill. "How small?" you ask? Well, it has a 15" table, about 5" wide, and is driven by a 1/4 HP motor. I have never stalled the motor, and I do work it reasonably hard from time to time.

The action of the high helix is to roll off tiny rolled-up "pins", and it seems that the shearing action is a LOT easier on the machine than the pounding of a plain milling cutter as it starts... There are always edges "in the work" with a slab mill, and it seems rather easy-cutting and low stress, particularly when you realize what is being taken off.

It probably is much slower in SFM than carbide is maximally useful for, but that isn't to say it would be like that for every machine and application. I run the slab mill in backgear, just like all larger cutters.

oldtiffie
09-17-2014, 09:11 PM
I have never seen or used a carbide slab milling cutter (TC was rare and very expensive in those days and were kept under lock and key).

Stellite was excellent as a substitute for YC and was even better for drilling really hard stuff.

All the slab mills I used were HSS which worked very well but required to be very well (and correctly) sharpened. Each job usually came with two cutters to allow for wear and a trip to the T&C grinders in the Tool Room to allow for re-cycling andf re-sharpening and to minimise delays to the job on the mill/s..

With all helical cutting such as slab mills (milling) and involute gear generator cutters (hobbing?) the reaction on the job to the cross thrust (along the arbor) required the thrust to be directed to the mill arbor taper roller bearing/s and NOT to the out-board bearing "hanger/s". This determined the direction of the mill table.

Longitudinal thrust resistance bracing was also added to the over-hanging bearing support bar.

Slab cutters are a total PIA when they have been successively ground and a lot of HSS needs to be removed - and this is when a careless Tool Room T&C grinder can over-heat (and "colour") the teeth of the cutter and then "hide" it with the last grinding cut.

https://www.google.com.au/?gws_rd=ssl#q=stellite

With nearly all and especially slab milling cutting the last/final cut was a "spring" cut - with "climb milling" cutting - to get the last "little bit" off (caused by arbor and job/set-up distortion "spring").