Mill reccomendations for a robotics team?

--Hiya; just caught this thread. FWIW head on over to mcmanis.com and ping Chuck who runs the site. He's active in the Silicon Valley HBRC and he's built a few battlebots as well.. Last time I talked to him he was organizing his own shop with mill, lathe, etc.

Gunner -

I sent you an email, but I'm cross-posting (right term?) in case you havent seen it ...

First of all, What would be the travel on this mill.. (im assuming its a 17x36 table)? Mainly because we'd love to have the capability to work on some larger peices. Second of all, This mill would be three-phase correct? then we'd need to get a VFD? or something else? Third of all, If we obtain a CNC mill, is there any way to operate it manually? Lastly, We're located in the Bay Area; how exorbitant would the shipping be to our school? (we're located in san jose ca).

Tatsunori Hashimoto

Perhaps not what you meant, but virtually all controls allow for MDI (Manual Data Input) programming. That is, you can just enter and execute one line of code at a time instead of writing an entire program.

Given standard canned cycles for facing, pocketing, shoulder milling, drilling, tapping, etc., I'd argue that one can MDI a part faster than one can manually machine it. This is even more apparent when the machine has an automatic tool changer.

The kicker, unfortunately, is that it takes the knowledge of a manual machinist as well as that of a CNC machinist to efficiently operate a machine this way. Looking at the picture Gunner linked to, the mill doesn't include the option for fully manual operation (no handwheels, for example). This makes the novice's life difficult because you're fighting with a non-intuitive computer while simultaneously trying to learn how to cut metal. Steep learning curve.

Regards,

Robin

Has not been touched on yet, but do you have access to a lathe?

If you are not interested in sub-tenths accuracy you could consider a DRO from Shooting Star Technologies.

I think that Robin's given some pretty good comments here.

Jim

Mr Robin - I guess my meaning was whether or not this cnc machine could still use the handles, I guess the answer is no. Although I feel very comfortable with CAD and programming, I'd still think that learning to code for cnc and learning to mill at the same time would be an unnecessary burden.

However, isn't there a way to use a handheld pendent type control to move the mill "manually" as if one was operating a power-feed machine?

Mr Rozen - We have access to a lathe (ie our machinist has one) but we dont own a lathe. We don't have the resources to buy both lathe, mill and their tooling (I dont think..) so although I know some would disagree, we're starting with a mill.

Also, we've considered the shooting star DRO and it looks to be very nice, however, we are currently considering a mill that has 20 inch of Z travel (travels are 30 1/8 , 12, 23.15 ) the shooting star DRO wont cover our Z travel... AND its also nontrivially expensive (at $749, we could get a small lathe). How does the accuracy compare on the Shumatech DRO with chinese scales attached? we're not likely flood cooling so fluid resistance is not that big of a concern

Tatsunori Hashimoto

The pendant basically allows the user to "jog" the machine manually. Essentially used only for setups. I have seen some seasoned machinists at work use the jog functions (with the little thumbwheel) to machine parts. The problem is that the wheel does not have precise control over the machine. There are lags and jumps where your feed is either too small or too large (50hp, 50000 lb machine rattles the floor in a 20ft radius) as the machine control tries to keep up with the thumbwheel and also accelerate/decelerate the machine to the correct position.

The bottom line is that you will be disappointed trying to run a machine with the pendant. If you're going to buy a CNC mill (in my opinion a mistake given the work and the environment to which it will be subject), you will need to learn g-code to write programs, and you will have to learn how to operate the control (setting up and running tools, programs, work pieces, etc.)

I'm fairly certain a manual Bridgeport (or knockoff) will machine everything you robots require, and you'll be able to make actual parts much faster with less learning and less frustration.

Unfortunately the only way you'll understand my perspective is to actually learn how to cut metal, and then learn how to use a CNC machine. I've done both. I've done more than a thousand hours on a manual mill and over a hundred hours doing setup, programming and machining on a CNC mill. Not a lot compared to many here, but enough to know that a student without much experience who is under a deadline doesn't want to fight with a CNC control to make a robot.

YMMV.

Regards,

Robin

It's not a bad choice, given that you have access to one elsewhere. You can perform lathe operations in a milling machine, which is actually easier and more effective than the reverse.

The Shooting Star instrument uses a piece of precision threaded rod as the spar, with a shaft encoder geared to run along the length. You can pretty much get whatever length of threaded rod you want. I suspect that setup is +/- 0.001 inch at best, so you can learn what you need to compare the two by simply inspecting the web pages for each to see the specs. If you want to cut costs, do not buy a three axis DRO, only do the X and Y axis.

Do not buy a lathe that costs 750 dollars. That would really be a mistake.

Jim

Well do not buy a brand new lathe for $750.00 . For students you might well find some kind business with an eye to the future willing to put you into a used one for that price . There are a lot of business people that are in a position and willing to help students out . Luck Ken Cutt

Apologies for the delay.

Any power tool can be dangerous. Because bandsaws pull the work down onto the table, they are _relatively_ safe. In contrast, you must read and understand "The Table Saw Book" or similar material before attempting to use a table saw - they like to throw work at high speed.

Mills and lathes are very powerful cutting tools, and have an ability to grab loose clothes, hair, jewlery etc., with potentially horrible consequences.

Flycutters cover a larger area than the typical endmill one encounters, putting the operator that much closer to harm's way than with an endmill. The tool bit on a flycutter tends to be less visible than the boundaries of a end or face mill, which you should keep firmly in mind when using them. However, don't get any where near any moving tool. Machining is not a forgiving activity.

With their cantilever bits, flycutters arguably add risk of breaking the tool. That is true of any tool, but also particularly true of any small endmill or drill bit. Wear safety glasses any time a machine is running.

The answer is "yes" if you remove the word "easily". Does that mean it is difficult? Not really, but there are many factors that can lead to errors, and once one removes too much metal, it's over. Do not expect to reliably hold +/- 0.001 inches at the beginning.

I have never used a dovetailed mill-drill, so I cannot comment on their accuracy and robustness. Somehow, I find it difficult to believe that moving the head on such a machine is equivalent to moving the knee on knee mill. As I said, don't take my word for it. With ER collets and reasonable care, I don't get into that much trouble. True, I do a few more edge finds than would be strictly necessary on a knee mill or perhaps a dovetailed mill-drill, but that seems to be the worst of it.

As for the bench top knee mills, I have yet to see one that matches the travel on my machine. Hindsight is always 20-20, but I would be hard pressed to find much fault with my mill.

I am not the one to ask. I first learned to use a mill in college, went back to it for some test fixtures in graduate school, and then more recently got sufficiently frustrated one day to type "home milling machine" into google.

Bill

This is where you need engineering input. You do not need to hold tight tolerances to get good alignment; you need to have adjustable mountings and have good alignment procedures, and/or use couplings that allow misalignment. Keep in mind that what starts out aligned might not stay that way under various loadings.

That said, I shoot for tight tolerances on everything I make. Failure to do so leads to a downward spiral of corrections for errors in corrections for other errors. I recently made a part with a channel that snakes from one side of the part to the other, with through holes connecting them. That required flipping the part and reading the drawing from the other side; it worked, but would not have been so "easy" had I been sloppy with the dimensions.

Good machinging is always desireable, but it is no substitute for good design.

I have no CNC experience, but my instincts align with those saying that manual experience is essential to CNC work. It would be very easy to instruct a mill to take a dangerously deep cut. There is a lot to be said for feeding manually before engaging a power feed, at least for rough cuts, and especially when cleaning up uneven edges.

In general, I suspect you would be better off without a DRO. If you want to learn, learn to navigate w/o one. A steel rule and a small drill bit allows you to get within 0.1 inches, at which point the dial readings become meaningful. A machine with uneven wear on its screws weakens this argument.

Bill

Thank you very much for your input.

I agree with all of you that we should definately learn without a DRO in order to understand the functions of the machine. That's something we'll figgure out later (whether or not backlash is a main concern for us.. I suspect it's not too bad compared to the other aspects)

Amongst the manual offerings, we're pretty much set on the chinese import shown at

because of the large work space (30x12x23 travel) and free shipping. Of course if we could find a

9x42 bridgeport for around 2.5k, that'd be a different story.

Am I making a horrible mistake here? Are knee mills alot better than dovetailed column mills? And does anyone have more suggestions as to what machines are good?

Thanks!

Tatsu Hashimoto

Update -

On craigslist, we found a Bridgeport mill with a DRO and KURT vise for

4k. Its in very good condition, and the ways are not worn. We've gotten arrangements for transportation (its only a 10 minute drive.. so it should be nice and cheap.) But the seller insists we pay him in cash.. is that a bit weird? or is that normal for machine tools.. (I'm not even sure HOW to get 4k in cash without setting off alarm bells). We've seen the mill in storage, and we know it exists, so its not a fraud or something. but still kinda strange.

Awaiting your opinion,

Tatsu Hashimoto

If I were selling it, I'd want cash. $4k is no problem at a bank. I seem to recall $10k is the alarm amount, although I recently bought a Mack truck with $10k cash from the bank with no problems.

Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

hobby pages are here: Severe stupidity is self correcting, but mild stupidity is rampant in the land.

-Ron Thompson

Hey Tatsu,

I assume you want to pay with a cheque. Sounds like he just wants to minimize his risk, which is understandable. But if it is because he does not have a bank account to deposit a cheque, or ID to cash it someplace, then there may be a bit more to his reason(s), and more than a bit of caution on your part would be wise.

Ask if he will accept a "Certified Cheque" as payment, paid on delivery to your shop floor, which should quiet your "alarm bells". You can show him the cheque prior to his loading it for the "10 minute drive", and give it to him when everyone is satisfied. Once written and Certified by the trip to YOUR bank, it is as good as cash to him, and if the deal falls through, you just take it back to your bank for a re-deposit in your account. Keeps the bean-counters happy too, and the cost is minimal to you.

Take care.

Brian Lawson, Bothwell, Ontario.

Re the transaction, get a certified check. IIRC, you want it made out to the seller (by name of course) or you, so that you can easily redeposit if you abort the deal.

$4k is a lot to carry around in cash. Not meaning to sound like a survivalist nutcase, but look into the concept of forfeiture. Fire, theft, etc., are also risks to cash.

Bill

Walk into the bank and withdraw it. To avoid alarm bells, have it in your account to start with, and don't hand the teller any funny notes or wear a mask...

Not a big deal, and perfectly normal when making transactions with people you don't really know that well - especially if you might be negotiating a bit based on condition, etc. If you think the seller is going to club you over the head and take your money without giving you a mill, well, shop elsewhere. Otherwise, bring cash if that is what the seller wants.

Certainly SOP for private transaction used cars, for instance. Likewise used lathes. Makes sense for used mills, too.

Cash - handy stuff, serves a purpose. Given the broad pervasion of fake cashiers checks as can be seen if you look up "Nigerian scam", it's hardly surprising that a person who does not know you from a hole in the ground would be happier with cash money. They _might_ take a cashiers check from a local bank - you could ask...

Hey, I'm the student machinist on Los Altos High school Eagle Strke #114 Los Altos, CA (we had that swivel drive last year at Silicon Valley, Sacramento, and Galileo Division at nationals). We have an Excello 602 knee mill we purchased last year and recently acquired the three-phase power for it. We purchased it off Ebay from connecticut, but there were some issues. Shipping is a large expense, expect to pay about $1 per pound (3000 pounds). Second, you need space (about 5 feet wide and tall) and the facilities to move and accomodate a 3000 pound piece of equipment (ie it won't fit through a standard 36 inch door). Finally, any piece of equipment you buy should be examined by an experienced machinist before you buy. Ours came sight-unseen and had several problems that took many days to solve. Finally, on a more general note, you need to look at training and experience. Several members of our team took machining classes at San Jose City College. Milling machines are large, dangerous machines that need training and experience to learn how to use. Another note, one of the largest difficulties faced by our team is acquiring tooling such as end mills. It is a substantial investment (1000's of dollars) and unless you buy new, sharpening and grinding is a major issue. Also consider things such as collets, a vise, and a clamping set. These are hundreds of dollars of things that are basic necessities for machining. Also think about liability and other issues related to the school.

CNC type equipment is another issue entirely. A DRO will significantly increase your precision and accuracy but needs skill to operate. CNC isn't useful without an excellent working knowledge of manual machining. Hope I answered your questions but think twice first. Michael Fagan Student Machinist Los Altos High School #114

contact me off-list for more info woodworker88 at gmail dot com