Trying to size a first mill

[Aaron_W]

People often fixate on materials thinking small lathes and mills can only work aluminum and brass. With a few exceptions that really isn't true, a decent small lathe or mill can turn many hard materials with care, just more slowly than a big machine.

Sherline and Taig both make nice small mills, but they are small. From what I've found a mill is more limited than a lathe when it comes to size a small lathe is mostly constrained by will it fit and does it have the power. Mills are much more limited by their rigidity. I have a Sherline mill and it is fine for little projects but rigidity usually becomes a challenge well before "it don't fit" does.

Really comes down to what you are going to do with it.

I have a Sherline 5400 3x12" mill (50lbs ish) and a Clausing 6x24" mill (700lbs ish). The Sherline does fine on the small model parts I bought it for, and I still use it for small parts. It has a higher rpm so works well with small drills and endmills so it complements the bigger mill. Drilling holes or milling small details it does just fine. Taking off lots of material or working on larger odd shaped parts was challenging, and it didn't take long before I started looking to add a bigger mill.

It is one of the few mills that you can legitimately pick up and put in a cupboard or under your work bench when it is not being used. I mean you could do the same with a 150-200lb mill but how many people will really do that more than once or twice.

There are a lot of options in between a Sherline and a Bridgeport, so knowing your limitations and needs will go a long way in helping determine what is right for you.
From a financial standpoint it is tough to beat a Bridgeport, there are tons of them out there so they are relatively cheap ($2000-4000 is not unusual). They weigh 1800-3500lbs so not a first choice for a shop in an upstairs bedroom. They are tall 7-8 feet which can also be an issue.

I like the size and capability of my Clausing so when these questions come up I lean towards the PM25 sized mills (727 728, PM30 etc), but I do like and use my Sherline so hate to discourage people from looking at them, just know what is realistic.

 

[mikey]

I guess what I'm really wondering, is could I "go cheap" on smaller Sherline machine to get started, and if I get hooked in this hobby I'd have more experience and know more about what I wanted in a next machine.

Answer: Yes, you can "go cheap" with a Sherline mill to get started provided your anticipated work will fit within the envelope of the machine. Sherline machines are not limited by what they can do; just on what will fit and allow your tools to access the part.

So, what couldn't I do on a Sherline? From other posts, it looks like it will handle aluminum and mild steel, which feels like it'll be fine for But if I had something harder occasionally, could the smaller machine handle it as long as I was patient and took light cuts? I also assume that I'm giving up some precision, but my guess is that since I'm learning most problems will be my fault. Is it possible to expect 0.001" precision once I build the skill and I'm careful?

A Sherline mill will machine anything a larger mill will machine, albeit in maybe smaller bites. I've milled mild, medium carbon and high carbon tool steels, stainless steels, aluminum, brass, plastics and wood without issues.

There are no rules regarding what a Sherline mill can or cannot do so I tend to push it until it complains. For example, my 5400 mill will take a full diameter slotting cut with a 3/8" roughing end mill in aluminum; that's 3/8" deep with a 3/8" diameter cutter without even slowing the motor down. That isn't a big deal on a big mill but on a mill that you can pick up with one hand that people think is a toy noodle, that's not too bad. I have taken a 0.125" radial depth cut with a 3/4" long carbide end mill in mild steel and hit the desired dimension dead on the first time. Of course, the mill will take lighter cuts also but it can do a whole lot more than even most Sherline owners think.

A Sherline machine is also quite accurate despite its supposed non-rigid construction. The last job I did for someone other than myself involved making a rear mounted parting tool post from aluminum for another HM member's Sherline lathe. I had to cut a slot for the blade and tried to cut it to depth with an end mill in one go but missed it by 0.0005"; took that excess off without a problem on the second pass using just the handwheels. Then I had to flycut the bottom to bring the cutter slot on the exact centerline of his lathe; missed that by a 0.0001" but figured it was close enough. The point is that greater rigidity does not confer accuracy in and of itself. My 800# RF-31 is certainly more rigid but it is not as accurate as my Sherline 5400, not even close. Where rigidity comes in is when you have to take big cuts with big cutters, something I don't do on my Sherline mill. Rigidity and mass also enhance finishes and can have a big impact on your boring capabilities and there is just no getting around that fact.

A Sherline mill is not for everyone. It has limited table travel and vertical clearance can be tight at times. Consider it only if your work envelope is on the small side. Just don't underestimate it.

 

[compact8]

I had to cut a slot for the blade and tried to cut it to depth with an end mill in one go but missed it by 0.0005"; took that excess off without a problem on the second pass using just the handwheels.

That's really impressive. Can you elaborate more on how it is done ? reducing the height of a work piece accurately by 0.0005" or 0.01 mm is kind of difficult on my machine because of the followings :

1) errors in bring the tool to just touch the surface of the workpiece - all the methods I have tried including, scratching ( with or without paper ) and Z-axis tool setter has an error of 0.01 mm or more.

2) errors of bring the tool down by that small amount - my DRO has a resolution of 0.005 mm so the error is of the same magnitude. Using the markings on the hand wheel will end up in bigger errors.

These two errors added up already exceeds 0.01 mm. How are they eliminated in your work ?

 

[mikey]

The big advantage to Sherline machines is the accuracy of their leadscrews and the accurate laser engraving on their handwheels. I simply lower the headstock below the desired cut level, then raise the head up to take up any backlash and carefully dial in my desired depth of cut as I come up. Sherline also has a locking lever on the Z-axis so once you set your depth of cut, you just flip a lever to lock it in Z and make the cut.

I don't have a DRO on my Sherline machines. I can easily interpolate a half thou cut with just the handwheels, or a 0.0002" cut or even less by eye. I may not hit it exactly on these low tenths cuts but I'll come close enough. If I need dead on accuracy then I'll use a tenths dial indicator to dial in the cut but that's not very often. The other thing I do with these tiny cuts is to dial up the speed a bit (easy to do with the variable speed of a Sherline motor) to lower cutting forces and reduce deflection. I always use a Beall ER32 chuck (confirmed at 0.0001" TIR) with a Rego-Fix nut, Techniks collets and quality end mills; this set up is very good at dampening vibration and maximizing accuracy. I suppose it also helps that my spindle also has less than 0.0001" TIR.

I don't think rigidity is a major deal with these tiny cuts but accurate leadscrews, proper speeds and the ability to feel the feed though the handwheels does make a difference. All of these things are strong suits of a Sherline machine. Add in a good tool holding system and the Sherline mill is a very capable machine.

My mill is over 35 years old. It has the original motor and drive belt, original gibs that haven't been adjusted in maybe 10-15 years and the Z-axis leadscrew and nut are nearly 20 years old. It is still as tight and accurate as it was when I bought it. In all the time I have owned this machine it has never broken or gone down and has punched well above its weight more times than I can count. And as good as I think the mill is, the lathe is even better.

 

[addertooth]

I will take this in a different direction. There are a lot of people that buy tools to make parts for models (train, car, plane). If the scale of your intended use is very small, then smaller tools make sense.

If your intended use is to make motorcycle/go-cart parts, then the size of *most* of your suggested mills may fall short.

I had to make a similar choice about a year ago. I ended up going with a PM 728vt. Some things that pushed me towards that model was the higher power motor, higher precision, one-shot oiler, and availability of well-engineered upgrades.

For the record, my lathe would be considered tiny. It may get up-sized in a few months. The lathe has proven accurate and repeatable, but the smaller through-hole in the spindle is (at times) limiting. When I got the lathe, the short bed (16 inches) did not concern me, as I intended to
make use of the through hole for longer parts. It has required I carefully design any projects, to ensure the parts using the through hole are 3/4 inch or smaller.

We both probably suffer from realistic limitations as well. I had limited space, and only 110v power available in the workspace. This drove my decisions as well. With small spaces, equipment placement is important, BUT also think of the use of the entire space. For the Mill, I integrated the table to also be used for a vise and assembly space. When you integrate like this, you get better use of limited space. Keep in mind when you are planning the space for the mill, you need "unobstructed space" for the full travel of the table to the left AND right. You must allow for that unusable space in your layout.

The final note is critical. Don't go cheap on cutting tools (like end-mills). Generally speaking a 3/8 inch, 48 dollar coated carbide endmill will last at least 4 times as long as a 12 dollar bargain end mill. I tend to like the end-mills which have asymmetrical flutes, as they are less likely to resonate on smaller (less rigid) milling machines.

It is a humorous evolution I tend to see. Many people upgrade to a larger milling machine AND also upgrade their cutting tools. They give all the credit for improved cuts on the larger machine, when a portion of the improved cuts can actually be assigned to better cutting tools. With a smaller and lighter machine, the quality of your cutting tools strongly drive the level of satisfaction. Avoid using those "value-bargained end-mills" for serious work. You will spend more money on better cutters, but in the end, it will be worth it. As a side note, I do have a bargain-bundle 2-flute and 4 flute (uncoated) end-mill sets. But, when serious work needs to be done, the more pricey end-mills get used.

 

[BGHansen]

If you decide to go the used route, try Facebook Marketplace which has more listings than Craig's List. Here are a few hits for a couple of lathes and a nice price on a small knee mill in your general area. I use the website "www.searchtempest.com" for CL searches.

Bruce

Upright knee milling machine - tools - by owner - sale

Great machine in great condition

yubasutter.craigslist.org

Metal Presision Gap Lathe Shenwai 12 in. x 36 in. - tools - by owner...

Shenwai Gear Head Lathe, Taiwan made. 12 in. x 36 in. cuts both S.A.E. & Metric threads, cam-lock chucks with 3 & 4 jaws & face plate. Two study rests. 1 1/2 hp. 115/220volts, 40-1450...

medford.craigslist.org

HF 10x12 metal lathe W/ quick-change tool - tools - by owner - sale

Ready to go, has tooling kit from little machine shop with boring tool, drill chuck, multiple bits and the quick change tool post. I am in over $1000 with the quick change kit. Don't make offers the...

goldcountry.craigslist.org

 

[Bob Korves]

Bigger machines can do bigger work, and do the small work as well. Small machines can only do smaller work. Try not to limit yourself more than is necessary due to work space and monetary issues...

 

[compact8]

Maybe the two attachments will help.

That's a very good overview article on mills. The article says "....the head on the PM-935 can be flexed up or down a few thousandths of an inch by hand pressure...." . Its quite a surprise for me that big machines can flex by as much as that.

 

[tghsmith]

what you are planning on making has everything to do with deciding on what size of tools are needed,, (budget also has a say in the deal) I know a modeler that does amazing work with sherline gear (brass, steel,ss) I build good sized models(live steam and others) some medieval crossbow parts.. my 2 LMS machines work very well for my current needs.. (and they will be easy to move when the time comes)

 

[krby]

Thanks for all the feedback! I should have included shop space in my initial post. It's not a dedicated shop, it is some open space in our attached garage, that is already pretty full. I don't see how to do a floor standing machine in the space I have. My plan was to put it on the end of a workbench, that will have enough space on the left and right for travel and stock if needed. Also, the more it costs initially the harder it is to justify for myself, also 120V <15A is a pretty hard requirement for now. If I end up loving the hobby, I could figure out getting 240V to right location, but it's a tough lift for now. Space wise, to fit something like a PM-25 or 728 or similar LMS, I would sell my stand-mounted drill press (nothing fancy, just a WEN) and use that space for the mill. It's open enough on the left and right to have enough travel.

Thinking about the times in the last 2-3 years I've thought that a mill or lathe would be useful. It's all small parts, aluminum or steel would have been fine. The biggest thing was wanting to put slots in 12x12x5/16" aluminum plate. The others were much smaller, a few inches across, brackets and such to fit existing things in the house. Several of these small parts might have been hard to shape without CNC, so that's another complication. I'm pretty comfortable with computer and electronics side of things, comfortable with Fusion 360 and g-code from 3D printing.

So right now, I'm leaning towards less expensive and smaller as a starter tool. From at least a few people who replied here it feels like for my personal hobby projects, it will do what I want for the next few years if I have the skill. The point about not going cheap on tooling is important, a less expensive machine helps me do that. I'm still thinking about this, not rushing at all. I'll try and cost out the options to get the out-the-door price and see what I would be spending. But, right now even the 50lb Sherline feels like a much easier tool justify given all the accessories I'll need to purchase regardless.

Quick follow up. The "bigger" machines in my original post use R8 while the Sherline machines all appear to be MT1. If I buy quality end mills, I would still be able to use them with an R8 machine in the future, right? I would have to buy R8 tool holders in the right sizes, but those cost a lot less than the mills themselves.