Steve

Thanks for posting this Topic of the Month. I am really interested in learning more about the operation of and tooling for milling machines. To start off the discussion I am posting the two videos that I filmed at the recent Heartland Hammer-In and uploaded to the ABS YouTube Channel.

[media] http://www.youtube.com/watch?v=rRYvvlp9vqc&sns=em [/media]

Bridgeport Type Milling Machines- Demonstration of features

[media] http://www.youtube.com/watch?v=ZW3KfSbtXn4&sns=em [/media]

Milling Vises - Selection and Use

I'll jump in. For knifemaking you don't need a very large mill BUT, kneemills like the bridgeport or the several taiwanese knockoffs can't be beat for versatility. If you can afford to buy new not a lot to consider(industrial auctions around here bring about $1000 for used). However if your buying used, check the guide ways for severe scoring and for lateral movement by tugging sideways on the table. Some of this movement can be removed by adjusting the gibs. Also check for backlash in the traverse screws. This also can be adjusted to remove some of it if the nuts aren't worn to badly. Iv'e used one of these at work for the last 20 yrs. and just replaced the nuts this year. The tabletop mills like the mill drills are useful as well ,I have one of these at home. The downside is you are limited to the vertical movement of the quill only. If you need to use a longer drill or endmill you have to raise the head so you end up losing your home position. As for the mini mills I don't have any experience with them but I'm sure once you get used to the size and limitations they might have they would be very helpful in the home shop.

Here is my advice from experience:

1.) If you don't have one - get one. Anything is better than nothing.

2.) When you can - get a better one. It doesn't have to be the BEST one - just better than the previous one.

3.) Don't ever listen to ANYONE if they tell you that the one you got isn't good enough. If it's better than the one you just upgraded from, then you did the right thing.

I'll add to this, since I've spent the better part of this year learning, researching, buying, and repairing mills.

I've got a 1939 Kearney and Trecker (Milwaukee) No 2 Vertical, 5hp, nmtb 50 taper, with rapids and power feeds in all directions. This mill weighs in around 4500lbs, but is shorter than a bridgeport, and takes up roughly the same floor space. If I could fixture a bridgeport on it's table, I could probably mill it in half. It took me a week to clean it up, adjust, etc, but with new oil, and some tlc, it's unstoppable. It's a truly industrial machine, made when they were built to last multiple lifetimes, and even though it's got a fair bit of wear, it's super accurate. These machines, like the old Cincinnati's, Van Normans, etc, will turn a cutter to molten lava before they'll chatter. In fact, my first few cuts I was having problems, until I realized that the mill feed was so strong that will would start ripping the 8" kurt vise off the table, if I didn't have atleast 4 bolts holding it in place.

I paid roughly $1000 for it, and they can be found all the time for scrap value or under, but you've got to know how to move them.

For face milling billets, and using larger cutters, brideports seem like toys comparably, however, the one big detractor, is spindle speed. The top spindle rpm on this one is 1400. It just wasn't designed for tiny 1/8" cutters, but honestly, neither were bridgeports. Using a 1/8th 4 tooth end mill, with a .0005 chip load per tooth, 150 sfpm, you need a 4584 rpm spindle speed, and 9.167 ipm feed rate, for coated carbide, you need to increase the sfpm 40% to be under ideal cutting conditions. Bear in mind, this is conservative chip load and sfpm, for over HRC 35 carbon steel, according to Niagara's chart. So for a coated end mill, you're looking at 6417, for carbon steel, which would be appropriate for damascus fittings. Afaik, most bridgeports top out at around 4k RPM spindle?

I'm no where near ideal speeds for 1/8th carbide cutters, let alone coated carbide. Honestly I'm not even in the ideal range for HSS with a 1/8th cutter, although it's certainly serviceable, and the rigidity gives it a huge edge over most bench type mills. On the other hand, I can run 4+ indexable face mills like nobody's business, and could practically eliminate the surface grinder from my equipment list.

I just acquired a nice MSC bridgeport clone. It's chinese, but was bought new in 1992, has a DRO, power table feed, etc, and minimal wear. Top spindle speed of 4k rpm and a great deal is why I bought it. I plan to use this primarily for fitting work and keep the K&T setup for facing and non-knife machining ops.

Bridgeports and their equivalents, are very convenient machines, and can replace a medium sized drill press (although they're not designed for the same type of loads as an equivalent horsepower heavy drill, and can suffer back-gear damage from heavy drilling), but in my area they go for pretty good money. $2-3k seems to be the average asking price.

If you've got the space for a bridgeport, you've likely got the space for a K&T or Cinci, and you can probably get a whole lot more mill for the money. My bridgeport clone weighs half of what the K&T does, but it's taller, takes up roughly the same space, and is top-heavy, so I actually found it trickier to move. The brideport type power feeds are very weak compared to the integral mechanical power feeds of the big mills, and while not ideal for smaller cutters, the big mills can be used for all sorts of other things like face milling damascus billets, milling ladders, and other patterns, etc.

Another thing to consider is that you can always mount a separate high speed spindle on a larger machine, which would give you the ultra high speeds for optimal carbide cutter use, while having a much more rigid set up than a smaller machine.

Like Karl said, if you don't have a mill, get one. Mills and lathes are the two most versatile machine tools, and even if you don't use them for much more than slotting guards on a knife, they open endless possibilities for making jigs, fixtures, tools, and anything else you might imagine.

Anyway, I got sidetracked writing this, so sorry if it's a ramble. My point is, don't think your only options are Bridgeports or import bench mills. Bridgeports are great, versatile machines, but they often suffer pricing based on their "name brand" appeal, there's much more robust american iron out there, and if you look at their "new" prices vs what they sell for now, they're a massive bargain comparatively. Get what you can, but I couldn't personally ever recommend buying a chinese bench mill when you could have a real mill for less.

I wanted to mention also, since I see a lot of guys recommending carbide cutters for slotting guards, that another concern with carbide is cooling. Coated carbide can be run dry in many cases, but will wear prematurely if you're not running the proper spindle speed and feeds. Interrupted cooling is a major no-no, so using a spray bottle or hand oiler, you actually run a huge risk of breaking your carbide cutters. So really, if you don't have the appropriate spindle speeds (many of us don't), and feed rates, and flood or other continuous dedicated coolant, you're actually likely to get MUCH better performance and life out of HSS/Cobalt/etc cutters than carbide. Carbide also needs much higher rigidity, since chatter, or cut interruption can cause it to shatter and chip. To run without coolant(with the appropriate coatings), they actually need the high uninterrupted heat that the high feed and speed rates give to keep from having chips weld to the cutter face, and provide optimal performance.

I know it seems like one of those "more is better", situations, it seems obvious that you should just use carbide since it's "better" than HSS tooling, but honestly, in most home shop environments, it's not. HSS holds up to more abuse, and lower tolerances than carbide, and really is a lot more forgiving, although it's important to buy good quality HSS cutters. Most of us can reach the required feed and speeds for coated Cobalt cutters, which can work really well in machines where intermittent cooling is standard.

So try a premium quality HSS or Cobalt end mill, with the appropriate feed and speeds before you waste money on a carbide cutter, unless you know for sure it's appropriate. Carbide is only "better" under optimal conditions, otherwise, it's actually worse usually.

Javan, I've been guard slotting with 1/8" Carbide and 1500 rpm for over a decade.

Rarely do I chip or break an end mill.

I wear them out first.

The one I'm using now I am sure I have milled at least 6 guard slots in 1/2" steel and stainless and even one in 1/4".

Well Karl, I wasn't trying to imply that anything less than optimal feed and speeds would absolutely result in crashes, chipping, or breaks with carbide. I was simply saying that those can be the results of less than ideal conditions. Rigidity (chatter), and interrupted cooling would be the most likely culprits for chips and breaks, not too low feed and speeds. Less than ideal feed and speeds though, do afaik, result exactly in less than optimal cutter life. I can't say what you got or would get from Cobalt, but I would kind of expect you to get dozens of slots or more from carbide in optimal conditions.

Anyway, not trying to act like a know-it-all, and I'm not an expert. I'm just the kind of guy that wants to know a "why?" that's a little more in concise than "that's the way so and so showed me", and most of the professional machinists I hang with, are always dogging on the ubiquity of carbide in home shop environments. Many seem to believe that outside of special circumstances or CNC, that really there's no justification at all.

Too me it seems pretty much the same as seeing the blanket advice to run a drill press at the lowest speed possible. With small drills, you're significantly reducing the life in many if not most circumstances.

I know some of us have a "whatever works" approach, and I don't mean to begrudge that. I'm just more the "obsessed" with learning the why's of things and so I wanted to share what I've gleaned. Not trying to ruffle any feathers. Hope it's taken in the constructive way it's intended, and if get anything wrong, please tell me why, I'll be the first to concede it. Most of you guys have way more experience than me at knife making, and I try to defer to experience, but it's hard to understand why I'm hearing completely different things from people with years of their life spent dedicated to milling operations.

*shrug*

No feathers ruffled here!!

I am in no way of the "whatever works" approach.

But I am of the "If it ain't broke, don't fix it" approach. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//tongue.gi f' class='bbc_emoticon' alt=':P' />

My meager mind just can not fathom all of those speeds and rates and so on, so I just turn it on and go!

If I break an end mill or a drill bit, I just get out a new one.

Yeah honestly, it probably doesn't matter when you're dealing with 1/8th end mills anyway.. The difference between Cobalt and Carbide is what? $2 maybe?

I just get a little obsessive sometimes, please ignore me when I do. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />

I have very limited shop space (my wife is an artistic blacksmith and our shop is one and a half bays of our garage) so buying an industrial mill on the scale of a Bridgeport is out of the question. I did purchase a bench-top mill made by a company called Sherline. I believe Uncle Al Lawrence (Riverside machine Shop) is now selling these mills. This is not a toy and with the proper tooling it can do everything I have needed a mill to do. From simple slotting of guards, to surfacing my Mokume, to cutting dovetails, to slotting the nail nick in a folder blade, this machine does it all quite well and takes up a fraction of the space of an industrial mill. I would suggest that anyone who is telling themselves "I really want a mill, but I don't have the room for it", to take a look at the Sherline 500A. Someday soon, I will purchase the Sherline bench-top lathe too. I just need to figure out where the new bench goes.........