New benchtop mill


#1

Hi,
We are looking to buy a benchtop mill in the offseason. Does anyone have any recommendations on which mills would be best for FRC use? Our budget is around $5000. Thanks!


#2

I’m just going to run through the standard CD checklist for mills:

1: Does it have to be a benchtop? Do you have room for a full knee mill like a Bridgeport?

2: You should probably count on spending at least as much on tooling as on the machine.

3: Do you have a mentor or a contact who knows how to use a mill? The nicest machine in the world won’t do you any good if you don’t know how to use it.

4: Whatever machine you get, it’s probably worth taking it apart and cleaning it up. You can look up details for whatever model you end up getting online.

5: At some point, Cory might post in this thread. If he does, listen to what he says. He knows what he’s talking about (much more so than I do).

6: The search feature is your friend. A quick search for “benchtop mill” produced a ton of results. Here are a few you might find relevant:
[1]](http://www.chiefdelphi.com/forums/showthread.php?t=129569&highlight=benchtop+mill) [2]](http://www.chiefdelphi.com/forums/showthread.php?t=98796&highlight=benchtop+mill) [3]](http://www.chiefdelphi.com/forums/showthread.php?t=78281&highlight=benchtop+mill)

It’s definitely worth reading through some of these old threads-- most of the info is still relevant.

Best of luck with your search!

Edit: Based on those old threads, I’d look into a RF-45. Grizzlys work but… Well, the one in the metal shop where 2667 works is pretty much perpetually broken and the Bridgeport has been trucking since probably before I was born, so make of that what you will.


#3

This thread and this threadshould be able to help you!

Also I did a little bit of digging around and I found this

That seems to be a decent mill with a Digital Read Out for really cheap (!!!)
I don’t own one so I can not attest to the quality of the mill however we have been using Grizzly tools in our shop for years and we’ve never had a problem.


#4

RF-45 is the highest quality readily available benchtop mill you’re going to find. It’s pretty pain free to use and can legitimately make good parts (especially with DRO), but it is small, doesn’t have much z-travel, and changing tools can be annoying.

It’s well within your budget, but you could also be looking at bridgeports/bridgeport clones with your budget, if you have space.


#5

Buy the most machine that you can afford and make space for, machine performance to price ratio is non-linear(eg. 2x$$$=4xMachine). If you want advice on tooling and/or buying a full sized machine used, please do not hesitate to PM me. Some people around here might say I buy too many machines >_>


#6

Seconded. The RF-45 has a dovetail column, which is a must IMO for drilling and milling on the same machine (which you will do). Whatever you go for, avoid round column mills.
Make sure you bolt these down, especially if you put them on the flimsy sheet metal stands they come with. I’ve found that as little as turning the handles too fast makes it shake and throws it off as much as 0.005" on the spindle.


#7

Who makes the best Bridgeport clone these days?


#8

Why benchtop when you have budget for a knee mill? Is tooling factored into the budget? A knee mill isn’t much more of a footprint on the largest benchtop type.

PM-940 from machinetoolonline.com would be my recommendation if you have to get a benchtop type. Ask about getting a variable speed spindle for it. PM-935 knee mill is made in Taiwan and would be even better if you can swing it. Both are 240V.

Enco has yearly 25% off sales that include machinery with free shipping. You could get a great deal on one of the knee mills if you sign up for their newsletter. I believe the Turn-Pro brand is Taiwanese.


#9

I was going to be going back through the content of these threads looking for some recommendation for 4901’s new machining equipment.

One thing I have to ask is there a good knee-mill that uses single phase power? There’s no way my team can get a 220V+ hookup in our shop.


#10

We have the same problem, we were originally looking at knee Mills, but we found we couldn’t meet the 220V power requirements.


#11

220-240V is typically single phase. 208-230V is typical three phase.

You can get static phase converters pretty cheap these days. If the motor is rated for inverter duty, you can get a variable frequency drive.

If you only have 120V available, there are VFDs for running three phase 208-230V motors, but you are limited in power.

A lot of knee mills are single phase, just check the motor nameplate.


#12

We only have 120V availible.


#13

You might be able to get a 1-1.5HP 208 3 phase mill and run a properly rated 120V single phase to 208V three phase VFD. Your maximum current draw (I estimate 9-10A for a 1.5HP on 120V) may be closer to the limit of the common 15A 120V circuit than you’d like.

I believe most knee mills use standard frame motors, so getting a working solution (120V motor) may not be that big of a deal. If it came between making a knee mill work on 120V or getting a G0704, I would get the knee mill and live with the 0.5-1 HP compromise.


#14

DO THIS. If you only have single phase 120V this is the WAY TO GO, its only a few hundred bucks for the VFD and its really easy to get a slightly larger breaker installed on the circuit you are using(go from a 10A or 15A to a 20A or 25A)


#15

Only if your wiring is rated for higher current is this a possibility (or within code). Otherwise, you are rewiring and you might as well get 240V run.


#16

I mirror the RF45 recommendation.
These have R8 spindles like the Bridgeport.
http://charteroakautomation.com/our-products/cnc-bed-mill/

That said, I have a highly modified Sieg X2 and have used the stock Sieg X3.
These have R8 spindles like the Bridgeport.
If you get one in good shape they can hold 0.001".
http://www.siegind.com/products_list/&pmcId=29.html
http://www.hossmachine.info/
Tool changer

I also own a ShopMaster Patriot VFD post-2012 mill/drill/lathe that I got for $4,000 with shipping used complete with CNC.
My machine takes 220V and has 1 VFD and 2 drive motors.
These have R8 mill spindles like the Bridgeport, MT3 for the lathe tailstock.
These machines support rigid tapping.
They can have sensors put on both the lathe and mill to ‘close the loop’ for RPM through the control PC.


The latest model just sold on eBay for $5,600 because a school ordered some and the funding fell through.

Also I’ve seen Tormachs here and there in the $5,000 range.
http://www.tormach.com/

I own both a MaxNC10 and MaxNC15 CNC min-mills with 4th rotary axis.
These are like Taig and Sherline.
They are a good tool for small jobs and could be used for jewelry making and aluminum gear making.
I wouldn’t necessarily make robot sides with it because the travels max out at 16".
http://www.maxnc.net/category_s/1817.htm

You want to make sure with the Chinese mills you can get support after the sale in case you have defects.
I hesitate to buy any used, ‘been laying around almost new’, Chinese mills because you don’t know they were ever tested.

You don’t need a mill deck the length of the side of your robot: if you put a guide on the back of the deck and dowel pins at the extreme travels. You end up with some extra holes but you can then support the over-length on rollers. Just tile the operations.


#17

Fair point, but I think in most cases bumping it up an extra 5A will be well within what the wire is good for.


#18

No. It is not.


#19

I will admit that that was a sweeping statement I made about the circuit layouts, sorry about that. You will often see smaller breakers in the panel than the wire can handle, before we had our former classroom turned shop rewired it had a LOT of 10A breakers when the wire gauge could have handled 15A.

If you have a 10A breaker, there are no problems on the part of the 14g wire upgrading it to a 15A breaker. A 2 HP(1500 Watts) Bridgeport at peak amperage being run via a VFD is 12.5A @120V even with efficiency losses you would have to be pushing that mill very hard to hit 15A (1800 Watts).

12g can be bumped to 20A (2400 Watts)
10g can be bumped to 30A (3600 Watts)


#20

I thought you were saying to change a 15A breaker to 20A. That would be a terrible idea. I have seen it done before and had conduit that was hot to the touch. Sorry for the confusion on my part.