Bevel Gear Machining.

[DonRotolo]

In the car world, the big advantage of spiral bevel gears are their much quieter operation and their somewhat longer life. The disadvantage is their higher production cost.

In your circumstance, I think ease of manufacturing would trump all that.

It is possible to make a flat straight-tooth bevel gear, but strength, durability and efficiency suffer. Really, the big gear is flat, and the pinion looks like a spur gear but with tapering teeth - the tooth profile is not constant, but gets thinner towards the far end. Generally the pinion is not very wide, maybe 1/2" - 3/4" for the kind of sizes I think you're working with.

Maybe try it with some machining wax, machining foam, or maybe soft brass?

[Orangedesign]

Hi FRC teams! As a team with little experience, we are trying to move away from imprecise tools. What would be a good and cheap 3/4 axis mill (~$2000)? Are used ones ok? Are complex parts manufacturable with better manual tools (ie manual lathe/mill)?

Many Thanks

[protoserge]

There are good inexpensive mills that can do the job just fine for most of the work an FRC robot needs.

We have access to a HAAS four axis once in a blue moon, but most milling last year was done using a Grizzly 1007 manual mill with an autofeed table. It goes for ~$1700. Harbor Freight has a slightly lower model as well (different paint and without autofeed) for $1100 (#33686).

Grizzly has some inexpensive endmills (~$90 for a set in R8 collet size). Spend the money on a precision machining vise. Grizzly sells some as well.

I would budget about $2500-3000 minimum for a good size setup considering the clamps, collets, endmills, cutters.

You can also retrofit one of the Harbor Freight mini mills (#44991) with a X2 CNC kit for <$2000. They sell the mini-mill for $600 and they may accept the 20% off coupons that are always floating around.


I'm sure there are plenty of other options out there as well.

I would post links, but I think that sends my posts to pergatory for now while I get my post count up.

[DonRotolo]

Used tools are OK, and can often get you much more machine for your money.
Search ChiefDelphi for many, many mill recommendations. I remember Dave Lavery offering a particularly good choice.

Far more important than the quality of the machine is the quality of the operator. An excellent operator can turn out world-class items from a poor machine, and a poor operator* can fail to turn out usable items from the finest machine on the planet.

Many schools / teams decide that CNC is the way to go, as a way of compensating for their inability to actually operate a milling machine. They let the computer make the decisions, and the result is just fine. I am of the opinion that having one or two kids on the team become excellent operators is a far better method.

So, find a local machinist or three, and see if you can get them to teach someone - ideally a Sophomore (who will be with the team a while) how to use a manual mill. And/or maybe introduce you to someone in the used machinery business who can find a nice machine with tooling (which costs as much as the machine!) that's within your budget.

My 2 cents.

*=almost any high school student who hasn't been taught.

[Cory]

Get someone who knows what to look for and find a used Bridgeport Series I/clone (Webb, Acer, Sharp, Lagun, Wells Index, many others) that's in good condition.

You can likely find an older one for about $2000-2500. This is something that's worth waiting and saving more if it means jumping from a Chinese benchtop mill to a US/Taiwanese/Spanish (Lagun) made knee mill. There's no comparison.

I would probably start with a lathe first if you have no machine tools.

[AdamHeard]

Better than any specific advice we can give you regarding machines is you that you need to find someone local (like a machine shop) who is willing to help you out.

Maybe they won't give money, or make parts; but they can still be incredibly valuable providing advice, old tooling sometimes, advice/training, etc...

Many of our shop sponsors never even run parts for us, but are invaluable for advice and fixes.

That being said, old machines of a nice brand in fair condition will be your best value in the machine market. You need someone experienced to help make that call though.

[MichaelBick]

Originally Posted by Cory

I would probably start with a lathe first if you have no machine tools.

I was going to ask our machine shop also, but I wanted the point of view from experienced FRC teams: if we want to get a lathe in the same price range ($2000 - $2500) what kind of lathe should we get. We will probably get the space for a full size lathe, but I would also love recommendations for table top ones in case we don't get the space.

[sanddrag]

Originally Posted by MICHAELABICK

We will probably get the space for a full size lathe, but I would also love recommendations for table top ones in case we don't get the space.

For years now, I've been recommending the Harbor Freight 44859 "8x12" lathe as a good benchtop model for those on a budget. I've had mine since 2006 and I have it on top of one of their 13-drawer tool chests which are also fantastic. The lathe actually measures 8x14 in size (according to how lathes are properly measured) and weighs a good 200 lbs or slightly more. I'd stay away from the 7x series import lathes. They're just too small. The 44859 has been a good unit with great precision and really no problems to note. It's a durable belt drive, with steel gears for the lead screw. It lacks a quick change gearbox, but how often are we doing thread cutting anyhow. If had it sitting right next to our refurbished 1961 Logan 11x24 which has been retrofitted with a VFD and QCTP, I'd probably most often still elect to use the Harbor Freight lathe just because it's a newer tighter machine that holds good tolerance and isn't worn out like our old Logan is. The HF lathe costs a lot more now than it did in 2006, but, everything does, and you can still try to get it with a 20% off coupon (one of my reasons for purchasing when I did). There may be a few things you'll need to do that exceed the size, rigidity, horsepower, etc of this lathe, but it can do quite a lot, even being on the smaller side. As a matter of note, the LatheMaster 8x14 is essentially the same machine with different paint.

[Mk.32]

Even better:
http://littlemachineshop.com/product...ly_special.php

One of our mentor has it, and I gotten to run a few parts on it it; pretty solid little machine. And as with any machine good sharp tooling makes a world of difference.

If you can house one, any Bridgeport or clone is infinitely better then any Chinese import desktop milling machine. If you don't have room for one, have a look at the RF45 Mill or similar and if even that is out of your budget LMS' http://littlemachineshop.com/3960 is a decent option.

And as the said above, having a guy that really knows how to run a machine is usually more important then what kind of machines to get.

Many schools / teams decide that CNC is the way to go, as a way of compensating for their inability to actually operate a milling machine. They let the computer make the decisions, and the result is just fine. I am of the opinion that having one or two kids on the team become excellent operators is a far better method.

This is interesting... seeing that CNC is a LOT more expensive and personally I find manual milling for basic parts compared to CNC usually as simple and sometimes faster. Though our new off season bot is almost 100% CNCed... heh.

[sanddrag]

Originally Posted by Mk.32

Even better:
http://littlemachineshop.com/product...ly_special.php

While this is a decent machine, I'm going to have to disagree with you here. Aside from this 7x12 having digital readouts and variable speed, the "8x12" (8x14 actually) is much more of a lathe than any 7x12 ever will be. It's physically about twice the overall size and weight, and can take a lot heavier cuts.

[Mk.32]

Originally Posted by sanddrag

While this is a decent machine, I'm going to have to disagree with you here. Aside from this 7x12 having digital readouts and variable speed, the "8x12" (8x14 actually) is much more of a lathe than any 7x12 ever will be. It's physically about twice the overall size and weight, and can take a lot heavier cuts.

OH... my mistake I didn't realized that the HF was a 8x12... heh
But yeah the HF is definitely a better deal