Mill reccomendations for a robotics team?

This is my first post, hopefully I haven't done anything horrible.

I am a highschooler (junior) at the Harker School (San Jose, Bay area, California), part of the robotics team there. We participate in FIRST robotics

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every year we build a 120 lb robot out of raw materials and compete against teams nationwide. Up until now, we've relied upon generous machine time donations from machinists in our area, but we would like to do machining in house (for both learning and time purposes, we only have 6 weeks to make our robot, and the lead-times for machinists are long). we've had everything from 6x4 plates with less than a mil of tolerance to 36 inch long tubing with about 10 mils of tolerance.

I'm here to ask you what you all think is a good mill for us to aquire. Space is not a problem, but we only have one-phase power wired to 15 amps. Although perhaps we can get the breaker changed, its unlikely we can get three-phase. Would we have to invest in a VFD? Also, I'd highly appreciate it if anyone could help us with how to find auctions .etc in the area.

Lastly, would a CNC retrofit be as accurate (if not more) than a simple DRO?

Tatsunori Hashimoto, Harker Robotics.

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Not easy questions to answer, as there are many possibilities. Used Bridgeport, but they're usually 3 phase, and converter, either solid state or rotary would be required. New, lower cost, KBC tools # VM-22-R8, ( would be a good choice, BUT 220V single phase. Motor could be changed out to 110V, possibly 1 HP without any great loss. Mill drills can do nice work, but depend more on the experience of the one using it than anything else.

Quick answer, the repeatability of a machine, to make identical parts within tolerances is dependent somewhat on the machine. How accurately a machine can work is dependent on the man running it. I've done some incredibly tight work on a mill drill, but that doesn't mean I want to do it again, only that it can be done. A good CNC retrofit for a mill will include ball screws to replace the lead screws, eliminating backlash. A DRO reads the actual positions of the table, both will reduce the errors caused by not considering backlash. (But so would a handful of simple dial indicators with mag backs on them, it just depends on how much fiddling you want to do before you start cutting.)

A machine that is poorly set up will do only poor work, and who made it, it's condition, will mean nothing. Again, right back to the man that's in front of it. Not having enough time to do it right the first time only means you'll find time to do it over. Cutting corners to save time will only mean doubling the time it takes. Cnc requires that you know the diameter of the cutter as closely as possible, Dro means cut and measure, then take the finish cut. In the end, the results are liable to be identical with one or the other. Cnc can produce complex curved shapes more easily, but that's something that's been done with other methods for over

100 years too. Cnc imposes it's own set of requirements, different from other methods, Other methods have their own set, mostly measure, measure, measure. Getting in a hurry is the mother and father of all screwups.


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Did you do the work or did the machinists do it for you? When I think back to some of the stuff I managed to do as a kid, nothing would surprise me, but I didn't know what a mill was at that time.

The reason I ask is that machine tools can be extremely(!!!!) dangerous. All readers of your post will want you to go through life with fully functional limbs. You need supervision, and from people who really know their way around machines. Further, I would greatly prefer that the supervisor(s) have experience teaching people to run machines.

A deadline can be a good source of motivation, but it can also lead people to take risks. Be CAREFUL.

On a 6x4 inch plate, I would try to hold 0.001 in tolerances regardless of the requirements, if only for practice, and because keeping things on size avoids a spiral of corrections for errors in corrections for other errors. A part that is 36 in +/- 0.010 is going to pose an interesting measurement problem - by interesting, I mean it will require some relatively expensive measuring tools. I think I would make the parts adjustable, and then either tweak until it fits/works, or calibrate the machine after assembly.

CNC adds another level and type of skill: beyond knowing how to run the mill, you will need to know how to program the mill to run itself. Mistakes can lead to dangerous forces on tooling and the work, and the fact that the machine is running itself, it is all the more difficult to detect. Note that I have never used a CNC mill, but I have this from good sources, and it makes sense.

A DRO simplifies some tasks. I have never actually used one. I started on an old Bridgeport mill, disappeared for a while, and am now doing quite a bit of machining in my garage on a mill-drill (a rebranded Rong Fu 31). It has a power feed, but no DRO. The more I work, the less I care to bother with a DRO. I will admit there are times when it would help, but it is no substitute for skill and understanding of machining.

I certainly do not want to discourage you, but if you have the money to get even a mill-drill and tooling, or the money required to get and ship even a used knee mill, then you are obligated to spend it well. I had to deal with lost mail, retailers recovering from two hurricanes, and a less than interested salesman, but it took a few months to select and receive a mill.

IMHO, it is not realisic for you to find, obtain, and learn to use a mill with six weeks to delivery of your product. Once you have a mill, keep in mind that the mill is useless without tooling. Some tooling is very expensive and "permanent" (unless damaged by collision with a cutting tool), other tooling is comsumable. You need an ongoing budget for tooling and maintenance, but you also need to know how to care for the machine.

Most important, you must have skilled supervision. It sounds as though you have engineers working with you. That's good, but many engineers are not machinists. My experience is that most engineers would be helpless in a machine shop. I know some glowing exceptions, and learned a lot from them. BTW, I am an engineer, so I can speak.

Good luck,


Reply to
Bill Schwab

What Bill said, and more.

The real value in the donated time you were getting was not the machine but the machinist. The 'lead time' for learning machining is measured in years. Presuming, of course, that you have a qualified instructor to help you keep all your fingers, etc. while you are learning.

That said, it still might be worthwhile to buy or even borrow a benchtop mill/drill for minor quick modifications. You will need a considerable assortment of cutting, fixturing, and measurement tools that will cost more than the mill/drill - the "borrow" option might provide all of those if you are lucky. And you will still need the qualified instructor.

If any machinists local to Tatsunori are listening: you should consider offering your time and equipment to help. I've done this and working with bright, motivated high schoolers is an absolute boatload of fun.

The kids these days are awesome, incredibly more aware and sophisticated than we were at their age. 'Public opinion' tends to be stilted by the press' choice to publicize only the dysfunctional kids. (Imagine that!! The press doing a bad job .... )

Reply to
Fred R

Silly question but there is likely a High School in your area that still has a machine shop and a Machine shop teacher with the tools and experience to help and get you guys started.

REGARDLESS of whether there are competing high schools in your school board cross school assistance when it comes to equipment is done and is reality because the school board owns the capital equipment. (Meaning all the inter school competition really doesnt matter when another school or team needs a hand)

Approaching the teacher to see if you could get some time or assistance from a highschool with a full machine shop would likely get you good results. or the VIce procipal or shop coordinators

Had i heard about FIRST earlier i'd have volunteered some of my time and machines for the idea where i am from. wrote:

Reply to
Brent Philion

Thank you very much for your insightful opinions, I appreciate it.

greybeard -

so would you say it would be easier to do work on a bridgeport rather than a cheap RF-31 milldrill because of the rigidity?

And is a DRO absolutely accurate? (ie reading on DRO always corresponds to table distance..)

We definately understand the need for careful setup; RC, our main machinist, always stressed the importance of setting up the work properly.

Also, how would you cut complex shapes without CNC? with a rotary table?

Bill Schwab -

We've used bandsaw, lathe at RC's shop but not a mill. How much more dangerous would a mill be? (fly cutters do look dangerous..). If we have this at our school, we'll definately have machinist supervision and instruction. I believe we have a few former machinists in faculty..

6x4 1 mil of tolerance is easily doable? or is it a fairly difficult task? I'm trying to gauge the relative difficulty of the work we do.

And as a user of RF-31, do you wish you got a larger mill or one with dovetail ways on the z axis? (we're looking at some benchtop mills.. from RF-31, Sieg X2 clones, X3 clones, and the mill at

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And our build season is already over this year (we shipped our robot on tuesday). I intend to learn how to use a mill (regardless of whether or not we acquire one) over the next year. (any suggestions? I've been thinking about volunteering at a machine shop..)

Thank you for your suggestion about having a machinist supervise us. We have a few machinists on facutly (who arn't being utilized because our school doesnt have a machine shop..)

Fred R-

I'd imagine that it takes many many years to be skilled at milling (our machinist says he's worked for 50 years..)

As for tooling, a graduating member is willing to donate to us R8 collets , vises, indicators and end mills. Of course we'd still have to buy alot of tooling, but I think we can get buy most jobs with end mills and a boring head (of course I could be terribly mistaken.. please correct me if I underestimate this)..

Also, what mill-drill would you reccomend? if its a RF-31, I've always wondered why one wouldn't get the sieg x3 (Grizzly carries it as g046) it has dovetail ways which means you dont loose your position..

Also, what other good ways of learning (for highschoolers..) do you know of?

Brent Philion -

We used to have a highschool next door, (a jewish school) with a machine shop, but we bought the campus and our school sold off the machines. Now I think there isnt a highschool close by with a machine shop (most of the ones I know have closed theirs..)

Thank you very much for your kind assistance

Tatsunori Hashimoto, Harker Robotics

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I just realized that I've never mentioned what material we work with.. We use 6061 aluminum for everything. The only steel on our robot is the gears and shafts. So the only real machining of steel we'll do is keyways. Does that change any of your advice? (esp concerning accuracy.. im guessing alu is easier to machine..)

Tatsunori Hashimoto. Harker Robotics

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Hi Tatsunori,

Be sure the school has sufficient pers I'm window shopping for my own machine, and inexpensive but idiot proof (BUT NOT CHILD SAFE !!!!) choices seem to be offered by MAX NC

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If you have a couple thousand to spend, I would recommend that the school buy the MAXNC 10 CL-B.

Essentially, the CNC has already been done for you in a hassle-free manner, and the owner evidently stands by his product. The only problem might be shipping expense, this place is in Chandler, AZ (about

5 miles drive from where I live).

I can afford to talk like a naive idiot (at least in the eyes of some of the people in this group and a lot of others) because not only do I have no pride left, I'm also not afraid to speak up and ask lots of questions just to learn... I've also found a friend who was a CNC mechanic but was laid off, he is willing to be my tutor until he judges me competent. Could be a while (he he).

Good luck,

The Eternal Squire

Reply to
The Eternal Squire

I think, judging by comments some of the skilled machinists here, that there is no end to learning the finer points. Even learning to make acceptable parts and fix mistakes takes a long time. The fact that you

*have* a 50-year machinist to talk to is a gift you should not take for granted.

That is Wonderful! It certainly means whatever you get must use R8 tooling. As for how much you need, it seems to me that I am forever buying yet another kind of cutter for milling jobs. One of the reasons I got a shaper was so I could do small strange jobs using hand-ground tool bits. 15 minutes grinding a tool blank from the bin-full on hand and another 30 minutes setting up and cutting. Way better than spending $60 and waiting a day or more.

In short, More = Better. Roughing and finishing, shorter and longer, various diameters. It does really help that you have somewhat standardized on 6061 Al since it is tractable to machine and you can focus on getting the cutter geometries appropriate for it. Delrin is another material you might want to have on hand; it cuts well with the same tools as aluminum and is great for sliding or rotating bearings against either Al or steel.

Another reason to reserve a budget for tooling: remember that cutting tools are consumables. Slowly when used correctly, very quickly if you make mistakes.

Speaking of ways, square ways do just as good a job as dovetails, they just need two adjustments instead of one.

I really think your best value would be to find a carefully used mill-drill. It will have the manufacturing leftovers (like the notorious sand in the headstock) already corrected and may come with more tooling. Try It is very active in your area.

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a Smithy combination machine that was listed Saturday and is sold already.

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a small lathe that would be handy for you as well.

Talking to and watching machinists is the best. Second-best is watching videotapes and then CAREFULLY trying it yourself. After that you try to stop the bleeding and figure out what went wrong. Then try it again. Repeat until crispy and golden.

Have a great time!

Reply to
Fred R

With respect, the worst advice I have yet read in this thread.

MaxNC machines are too small and flimbsy to put up with ameteur machinists. CNC is *not* required or recommended(!). A good manual machinist is required to make a good CNC machinist, period.

I would recommend a Bridgeport or knockoff. You'll spend the least amount of time messing around with the machine, they are the most tolerant of mistakes, and they are the most rigid of the mentioned machines (desktop, benchtop, floor).

Personally I like a heavier machine with a more powerful motor and faster spindle for manual aluminum work, but the BPT will be a good match for the type of work being described.



Reply to
Robin S.

It is always benificial to have the largest, most powerful machine that will fit in your space, is within your budget, and will hold the part you're machining.

A bridgeport is ideal for your work. A mill/drill is a compromise (less rigidity and smaller capability in exchange for less money and smaller footprint).

As far as the work you're doing is concerened, yes.

What kind of "complex" shapes are you producing? Can you specify examples?

It's not a matter of degree. A bandsaw will cut your finger off while a mill may pull your finger off. Neither are ever acceptable. Both machines require respect and proper training.

Truly +/-.001" on a bridgeport is pretty tight, but certainly attainable. What kind of work are you doing that requires such a tolerance?

Here's a rule of thumb: 1st and 2nd year apprentices are considered losses (pay and overhead versus output). 3rd year apprentices might break even. 4th year apprentices should make the company money.

If you happen to find someone willing to let you work in their shop (costing them money! even if they never give you a dime), ask as many questions as they'll allow, do your best always, and always be respectful of that person's sacrifice as well as their experience and capability compared to yours.

*Important advice below*

Make a point of designing parts around the tooling you have. Cutters get expensive *very* quickly and you will inevitably run out of time. If you want to keep the price and complexity of your parts low, Keep It Sweet and Simple (KISS).

You're in a rough position.

In high school, I entered two Canada-Wide Science Fairs with projects I had built in machine shops. I was lucky because of the people and facilities to which I had access. I'm sure you've seen that there are many skills that you have to master to be successful in large projects like a robotics competition. Time management is huge. Conceptualization, design, fabrication and assembly of the project. Perhaps a write up. Computer programming. The list is endless. Adding machining is a big jump, but if you can pull it off you'll be far ahead.

Good luck with everything. Enjoy this time, as you are working towards your own goals. Once you start making parts for other people, it'll never be the same.

(Go for the Bridgeport, if you can)



Reply to
Robin S.

With respect, the subtext of the original request is not fully understood by my distinguished colleage somewhere else out there on the Internet.

No matter how well motivated or cautious or intelligent or bright a high school student is, legally and morally that student is still a minor. Special considerations apply.

The intended operators are not amateurs, they are children. Bridgeports and related machines will almost certainly exercise lethal forces in the event of an accident. While smaller mills can generate lethal forces, due to physics the amount of total momentum applied against any part of a child's anatomy will certainly be less. That increases the chances that the ER team can save the child in time.

These children do *not* have the time, let alone the attention span, to become good machinists. They best they can do is a 13 week semester (never mind the 6 week deadline) is to develop an appreciation of the basics. A good manual machinst, however, should be required as an instructor, simply for safety reasons.

Probably for legal and liability reasons, the students should not even touch the machine. (Sorry!). A hands off approach would then mandate the use of CNC. The students can develop an understanding of the parts of the milling machine, draft CAD diagrams, download, and run in the presence of the instructor.

Can you image how high the school board would go ballistic when they hear that you want to reintroduce the machine shop? Selling the idea as a computer controlled demonstration that could fit on a desktop, with live demo at the board meeting, would go a LOT easier with them.

Save that for college or vocational school.

Reply to
The Eternal Squire

I agree.

I bought a MAXNC-10 for my electronics business thinking it would be useful for making test fixtures. The small working area, tiny spindle and steppers and slow speed have caused it to be nearly useless to me. I've had a couple chumps wanting to buy it, but I'd feel guilty if I sold it.

A bridgeport or equivilent would be good. Next on the list would be the cheapest knee mill you could find with an R-8 spindle.

Reply to
Jim Stewart

Explain your reservations to the chumps before the sale, if that be the case - but they may have different needs/expectations, and if they go in with eyes wide open, you have no need for guilt, some money, and less space being taken up by nearly useless objects.

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Perhaps "special considerations apply" but the size or power of the machine has nothing to do with it.

Uh, they are amateurs. Call them children to their faces.

Absolutley wrong. *This* is what's wrong with the internet.

I've run a Taig milling machine (essentially a MaxNC without CNC), Bridgeports, 3 ton horizontals and 30hp CNC machines. My Taig will cut your finger off just as fast as the 50hp CNC machines at work will.

Tell me your experience with milling machines. I'm guessing you haven't run a mill for more than a dozen hours. I've got 5,000 hrs of my tool and die apprenticeship done. I've about 1,000 hrs on bridgeport machines and about

150 hrs manually programming and using CAM software to program CNC mills.

Then they *certainly* don't have time to become decent CNC machinists. As I said, you have to be good on a manual machinist to perform on a CNC machine, period. Ask me how I know.

They shouldn't be allowed to walk on the sidewalk or ride in a car either. Very dangerous activities (bridgeport is 1hp, smallest common care engine is about 100hp).

Bullshit. Will the teacher saw off the stock for them? Put it in the vice and set up the mill? Perhaps program the machine because there's not time to teach the *children* how to do it? I guess we'll just let the students press the green button.

Great learning experience. Indeed you've entirely missed the point of school.

They can setup their manual mill and crank the handles as well. It's not rocket science and it isn't dangerous when the student has proper training. Many Europeans start their apprenticeships well below 18 years old.

Great. Buy a machine that DOESN'T have the capacity the students need, requires programming and setup skills they DON'T have and probably costs more than a used knockoff bpt.

Great idea. We need more great ideas like that in industry too.

There are those who say, and then there are those who go and do (as the sayers watch). The student asked what kind of mill was required for the type of work he is doing. A MaxNC WILL NOT DO THE WORK REQUIRED. That's the bottom line.



Reply to
Robin S.

You should try that for yourself...



Reply to
Robin S.

of the floor models..they rank pretty low on the rigid scale.

If he were in California..I could probably get a company to donate a Shizuka CNC knee mill with a Dynapath 10 control. Runs pretty well, but the spindle bearings are likely to need replacement. Located in Monrovia California

Cross posted into alt.machines.cnc. Mostly pros there..may have some input


"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."

- Proverbs 22:3

Reply to

Are you talking about the open loop, or the closed loop MaxNC 10? It is true, the open loop is only good for PC boards because of the lack of torque.

I just got off the phone with MaxNC closed loop machine today. I asked a fair number of questions very carefully:

1) How precise? 2) How accurate? 3) How tough? 4) Can I mill PC boards with it? 5) Can I mill aluminum boxes with it? 6) Can I mill small steel parts with it?

With qualifications, all the answers are yes for the NC10 closed loop.

The technician told me that with the closed loop the precision and accuracy are both approximately the same, zero dot 2 thousanths of an inch. The closed loop can exercise about 8 times the force as the open loop, and one of the customers is milling mini turbine blades from hardened specialty steel for a model jet engine.

And from the way he talks he is hardly a jumped up Walmart hardware store salesman.

Those who do are called artisans Those who say are called researchers. One can't exist without the other.


The Eternal Squire

Reply to
The Eternal Squire

Thank you very much for your all's time.

As for MaxNC, that's out of the question for us since we'll end up frequently manufacturing parts greater than the 12 inch travel. For the safety question, we've gotten a ok for a manual mill as long as there is a machinist watching over, and there is restricted access (to ensure some of the more careless members dont play with it like a toy). We've also been fairly careful with our handeling with machine tools and even though it is a risk, we think its one worth taking (for the things learnt).

" Truly +/-.001" on a bridgeport is pretty tight, but certainly attainable. What kind of work are you doing that requires such a tolerance? " We manufacture our own high-speed gearboxes whose mounting plates require about 1/1000th tolerance. we've previously found that even

1/1000th off can cause the motor to bind and start flipping the breakers, or cause unacceptable current draw.

As for the mill, we are in fact located in California (bay area, however.) , so we are highly interested in Gunner's offer of a Shizuka CNC mill. If that is not possible, we can of course, go for a bridgeport, or we've also been looking for something like

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the square column mill. The work envelope is more than adequate, it seems to have a strong enough motor for our work, and the spindle speed seems okay for aluminum work. the Free shipping also makes it very attractive for us.

Tatsunori Hashimoto

Reply to

As this was Tatsu's first, this is also my first post. Who knows, I might get this right.

Anyway, I am student mentor for Tatsu's team at the Harker School. I have had a good bit of machine tool use, and could say I am decently proficient with manual and cnc mills. The robotics team is looking to get about a bridgeport sized mill, but not a full knee mill. The one that Tatsu posted a link to, from industrial hobbies, is a chinese import mill with a decently sized travel (12x30x 24 vertical) and R8 taper, with a 2 hp single phase motor. This mill basically fits into all of our requirements, and is what we are seriously considering getting.

Gunner, thank you for your offer. We will have to see with the school if it is at all possible to house something like a full-size knee mill (I am guessing it is the size of a normal bridgeport).

I agree with all of you who say that a student that doesnt know how to manually mill doesnt know how to CNC. I learned the hard way first, on a 1967 bridgeport with no DRO. I have gradually worked up from then... but I do believe that a high school junior or senior could be taught to mill decently in three months. The kids at Harker are bright, I have seen several outstanding examples. Of course, not everyone would be even allowed to touch a mill, as Tatsu said.

We plan on having a mill, 3 axis DRO, milling vice, clamp set with t-nuts and studs, rotary table, boring head, indicators and edgefinders, end mills, full tap die and drill sets, mill vice parallel bars, a nice keyless chuck, center drills, calipers and mics, carbide insert face cutter, some reamers, and I am probably forgetting something. Anything else we might want to get?

Currently my main concern is getting a DRO without selling an arm and a leg. Would anyone have suggestions on DROs and where to get them?

Thanks, Veselin Kolev

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