Category Archives: Starting Your Own Shop

Bridgeport CNC Conversion – Is It Worth It?

Converting your manual mill (Bridgeport) to CNC is a cheaper way to get into running production runs. While manual mills can still be useful in shops today for certain operations on one-off part, they are virtually obsolete for production runs if you want to make money. However, if you are starting up a small CNC shop of your own or are a hobbyist on a budget, a CNC conversion kit may be your answer. However, lets take a look at what it will take to convert, how much it will cost, and how it compares to a a VMC (vertical milling center).

Conversion?

You can buy a CNC conversion kit and piece it together yourself, or you can buy a mill that has already been converted. Of course buying one that’s all set up and ready to go would be ideal, but you may not have that much cash to spend right away. This is why many machinists end up buying the parts as funds allow.

If you want to convert your Bridgeport (or similar) manual mill to CNC, I suggest doing a full 3-axis conversion. It will be more expensive, but if you are going to do the swap, you might as well go all the way. Being able to program for Z-axis moves in addition to the X and Y-axis will allow for shorter machining times.

Bridgeport CNC Conversion
Bridgeport CNC Conversion

So how much will it cost? A knee-mill (bridgeport) converted to CNC will cost anywhere from 10K-25K. The newer and nicer set-up the more expensive it will be. Shopping around and waiting for deals may help lower that cost, but you should still expect to end up in this margin for a ready-to-go mill.

Buying a VMC

While buying a vertical milling center will be more expensive in most cases, they are much more capable machines. Faster rapid moves, a lot sturdier, more horsepower, coolant, automatic tool changes, and the list can go on. It really depends on how much you want to spend and how big of a machine you want. $20k can get you a used CNC mill, but it will probably be 15+ years old and will need a lot of maintenance sooner rather than later. For another 10-20 grand you can get a newer and nicer machine that will actually last a while depending on how you use it and what kind of deal you get.

What Do I Recommend?

Without a doubt, a VMC is the better choice IF, and that’s a big if, you have enough dough. Of course, many of us that are middle or lower-class citizens cannot just throw $30,000+ at a machine at any given time. This would be a long-term goal, but the capabilities are are vastly greater than a converted knee-mill.

I Should Buy/Build A Converted Manual Mill If I:

  • Am on a budget
  • Have time to convert it as funds/time allow
  • Am just a home hobbyist
  • Want to DIY to save money

I Should Buy A VMC If I:

  • Want a faster, sturdier, more powerful and capable machine
  • Want to make a business out of it
  • Have a bigger budget
  • Have patience to save up for one (If funds don’t currently allow it)

There’s advantages to buying each kind of machine. While I haven’t said which one is better for YOU specifically, I have tried to lay out reasons why you would or wouldn’t want to go a certain route. If you have any questions, feel free to post a comment.

Mini Desktop CNC Mill – Pros & Cons

CNC mills have progressed so far these days that you can have your own milling machine that can sit on desk or benchtop; hence the name ‘desktop cnc mill’. Depending on how much you want to spend, you could have a set-up for the price of a new computer.

If you are willing to dedicate a good amount of time to learn how to program and use software, having a desktop cnc machine can be a great asset, whether you’re looking to make your own parts/tools as a hobby, or actually turn it into a small business.

So, lets look at the what makes a benchtop CNC Mill an advantage over a full size machine, as well as how they are at a disadvantage…

Pros

Cost

Compared to the price of a new 100,000 dollar milling machine, you can get a mini CNC mill for a small fraction of that. How much do they actually cost? I can’t really give you a good estimate because there’s so many options available. You could buy a basic kit that’s complete for less than a thousand bucks, or you could be a bigger and better machine that’s fully enclosed with more bells and whistles for a few grand.

Fully Enclosed Desktop CNC Mill
Fully Enclosed Desktop CNC Mill

Technology

For the price of a desktop mill, you get a lot of technology, especially if the package comes with a good CAM/CAD software. In the past, you’d have to buy a big manual mill or lathe and convert to a 240 set-up for electricity in the garage/shop. They are not enclosed, so after machining a part you’ll have a big mess to clean up, whereas a desktop CNC can be enclosed so you have little to no cleanup afterwards.

Size

A big advantage of a desktop mill is how small they are, hence the name “desktop” or “benchtop CNC”. Instead of requiring a large garage or pole building to set up a milling center, you can put one of these in your house!

Cons

A desktop CNC mill may be able to machine parts just like a full-size milling center, but there are some pretty big disadvantages. This may or may not affect you, though, depending how what kind of machining work you plan on doing.

Mini Desktop CNC Mill
Mini Desktop CNC Mill

Size

The size of these machines can be a good thing, but it can also be a downside depending on how large the parts are that you are going to make. If you want to make motorcycle rims, a desktop machine just isn’t going to cut it. Not only is the machine itself too small, but you may run into rigidity/machine capabilities if you are removing large quantities of material, which brings us to its next downfall…

Capability Woes

Unfortunately you won’t be able to hog out stainless or hard still parts on most of these mini mills due to the fact that they are not nearly as rigid as a full size machining center. A lot of them are only built to machine plastics, wood, and soft metals such as aluminum. If the metal is too hard, it will cause a lot of spindle/tool vibration, causing poor finishes. It may also end up breaking your tools because the machine cannot handle the extra tool pressure.

Machine Shop Rates – What’s the Average Hourly Rate

If you want win in this competitive market, you have to be on top of your game by being efficient. Depending on what kind of jobs you’re running, you want to run the best equipment and tools for it, as well as utilizing them properly.

Fortunately, this doesn’t mean you need to buy the most expensive machine. As a general rule, the more complex the part, the more you’ll have to spend on precision equipment. On the flip side, you can charge more because it takes more time and money to run the job.

What Machines Are In The Shop?

There are a lot of factors that can determine the hourly rate of a shop. Shops that can utilize bigger are more powerful machines will generally charge more because the overhead costs are higher, and they can do more than just a small job shop with lesser machines.

What Kind of Shop Is It?

Comparing hourly rates of job shops and production shops can vary greatly. Running production is usually a larger shop with big machines that can run dozens or even hundreds of parts at a time. Efficiency is very important, and rates will often be higher. However, the orders can be started and finished in a fraction of time.

Smaller job shops that do more prototype parts and small batches are usually a little cheaper. However, the cost per part can be quite a bit higher because set-up time is expensive. The more parts you run, the lower the cost-per-part will be.

Quality or Quantity?

Just because a shop has bigger and more powerful CNC machines does not mean it is a better shop. A small 3 man shop can be head and shoulders above a 20,000 square foot machining shop as far as quality goes. In order to meet or exceed the customer’s request, there must be at least one machinist in the shop that knows how to do that. You can’t just make a program on a CAD/CAM system, load it onto the machine and expect everything to run perfectly. In fact, programming is sometimes one of the easiest part of machining.

The difficult part is making a fixture that properly holds the part, choosing the right tools for the part (size, length, material), as well as speeds and feeds that will be the most efficient (shorter cycle times are good, but if you’re burning through tools every few parts, you’re spending more on tools and down time because you have to stop running the machine and set a new one up; Time = Money). Some characteristics of a well rounded and skilled machinist can be found here.

Lets See Some Numbers!

Currie Engineering
Currie Engineering

So, you want to see some actual dollar amounts for machine shop rates… There’s a few different ranges of numbers, and as a general rule, you get what you pay for. $40-55/hour is considered cheap in the manufacturing industry, and while you may be able to find a local shop that has a rate that low, their work will probably reflect. However, if you need to make parts with wide open tolerances, you can save a lot of money going to a company that is 48 bucks an hour. Manual mills and lathes may be the majority of machines found in a shop like this.

60 to 80 dollars per hour is the average machine shop rate in most parts of the U.S.. Electricity is and overhead costs play an important role in what a shop is charging. However, the most important factor would be quality and type of shop. Prototype and short run parts are expensive due to set-up times. If you need to make a part with tight tolerances, that will greatly narrow the choices down. The shops that are able to make high precision and good looking parts know that, and are able to charge more because other shops can’t compete with their quality.

If you were wondering about the top dollar shops, there are some out there that charge $100/hour and beyond. Why? Along with the above mentioned, the high cost is because they are large shops with multi-million dollar machines that produce a high overhead to run, including well-experienced machinists that often get paid a better wage because of their expertise. It may seem ridiculous if you’re new to the career, but if you add up all of the expenses of machines operating, tools, inspection equipment, coolant and chemicals, electricity, and obviously the machinists/programmers themselves. After adding all those numbers up, they shouldn’t be more than what the company is making per hour, especially if the owner wants to make a profit.

In the end, it really depends on the kind of work that is being done. The higher precision and meticulous that stand strongly behind their quality will charge more, but if you have fussy parts, it is well worth the cost as opposed to rejecting the same part from a lesser shop that can’t meet the tolerances.

CNC Machine Shop – What Is In It?

While every machine shop is different, you’ll see similar set-ups when you walk through them. There will usually be the main area where all of the CNC milling or turning centers are, as well as a section to deburr parts. Sometimes there will be deburring tools/machines next to the machine you’re running if the operator does all of the deburring.

Usually in a different area there will be a stock room with all of the raw materials needed for upcoming jobs. These few rooms or areas make up a CNC Machine Shop, which is usually a large industrial or steel building, as well as a small pole barn or garage, depending on how big the company is.

Stock Room

Round stock, square stock, and tubing are the most common, and they are usually 8 or 12 foot bars in length. There should also be a band saw in this same room so that someone can cut up the right size stock for each job. Most shops have an automatic horizontal band-saws so that they can cut a large quantity of parts in a short period of time with relatively close tolerances.

Machines

Machine Shop
Machine Shop

Depending on what kind of a machine shop you’re in, there’s a lot of milling machines that could be running. While milling and turning centers are the most common, there’s many more machines, as well as different variations of each.

A shop can have vertical or horizontal milling centers, depending on how complex their parts on, and if they’re a job shop or a production shop. Vertical mills are the most common because they’re cheaper and easier to use and set up.

Lathes are pretty similar, but they can be a flat-bed, slant-bed, multi-axis, or have live tooling for special jobs.

Other machines include, but not limited to: Wire EDM, waterjet, press brake, turret punch, CNC laser, as well as miscellaneous deburring machines (tumbler, straightliner, grinders).

Deburring

Like mentioned above, there will be some deburring tools/machines if the company wants to save money by doing all or most of it themselves. Often times there will be a drill press and grinder next to each mill so the operator can do most of the deburring right there in between cycle times.

The higher quality and quantity the parts, the bigger and better the deburring equipment will be. Giant tumblers/vibratory tubs are often used in large production shops for basic deburring. Media blasting is also common for parts if they are to be plated or coating with something. Zinc, chromate, anodizing, hardcoat/powdercoat, and nickel are just a few coatings that are done to machined parts to give them a better look, last longer, and/or function different.

Inspection Room

Clean Inspection Room
Clean Inspection Room

The inspection room should be separate and enclosed from the shop. If parts have close tolerances, there will be expensive inspection equipment, and the room will be temperature controlled so all of the readings are accurate and consistent.

Tools will include: a granite surface plate, height gage, CMM, bore gage, go/no-go gages for specific jobs, optical comparator, profilometer, thread gages, and gage pins. Not every job will have all of these tools, but some will have more.

Depending on how big the shop is, you (the Machinist), may or may not be inspecting your own parts. The more machines and tools you learn how to use, the better off you will be, so try to get in on how to use the equipment if there is an inspector at your shop.

Well, that’s the jist of what a CNC Shop has on the inside of it! Check out my other articles for tips on becoming a CNC Machinist. Stay tuned for more…

Used CNC Milling Machines – What To Look For

Looking to start your own little shop with a CNC milling machine? They can be used to make extravagant parts and turn huge profits if operated by an experienced CNC Machinist. However, if you don’t know what to look for or have proper training, a machine can turn into a very expensive paper weight in your garage.

If you know what you are doing on a CNC machine and are serious about starting a small shop, lets take a look at some things that you should be on the lookout for when buying a used machine. You don’t want to spend thousands on a milling center only to have it need thousands more in maintenance done…

Age

Obviously, the newer the machine the better, as an older one will inevitably cost you more money due to higher maintenance. How efficient do you want to be, and how big is your competition? If speed is not very important, a CNC mill that is 10-15 years old will get the job done, assuming it is in good shape.

SizeOLYMPUS DIGITAL CAMERA

How big of a machine do you need? How big are your parts going to be? Do you have room in your garage/shop? Remember that you have to not only include the machine dimensions, but an additional amount of space around it as well. A common machine will have 40 inches of travel on the X-axis, and 15-20 on the Y-axis. Don’t need something that big? There’s some that are 30 inches, and the mini/tool-room mills have 15-20 inches in both directions. Price coincides with size, so if you are on a budget, get the smallest one possible. This will also allow you to find one that’s a little newer, due to it costing less than a bigger machine.

# of Tools

How big of a tool changer do you need? 10? 20? 40? ATC’s (automatic tool changer) come in a variety of sizes and locations. Smaller carousels that have 10 or 20 pockets are often inside the machines enclosure. If you need one with more pockets or on the outside of the machine, it’s going to cost a little more.

Spindle Hours

The number of running hours on the spindle is an important factor to consider when looking at a used CNC milling center for sale. Machine on time isn’t as important because the spindle won’t be running or feeding. The seller must be able to show you how many hours it has. If they don’t, they’re probably trying to hide something, so it’s best to steer clear from that machine. Under 4000 hours is a good start.

Options

Although options may not add a lot to the value, it may be harder to find the exact machine you want. Some of the popular options on CNC mills are: chip auger, rigid tapping, tool setter/probe, high-speed machining, high-speed spindle, larger coolant tank, coolant-through spindle lines, 4th axis, faster rapid movements.

It all depends on what you need the machine to do, and how patient you are in finding the right machine. The longer you wait, the more deals will show up.

Controller

Are you accustomed to a certain machine controller? If you need a specific brand/model, that will either cost more, or will take longer to find. Fanuc and Yasnac, Fadal, and Mitsubishi are common CNC controls. While they are able to do a lot of the same things, navigation and codes can be quite a bit different. If you’re not sure which one you want, doing plenty of research before will save a lot of time and hassle in the long run when you actually buy a machine.

Noises

It is important for you to go and look at the machine prior to purchasing it. If it is out of state, find a professional or someone you trust to look at it. The seller may be hiding something that can only be  noticed when the machine is running.

Run the spindle and various speeds and listen for any noises/humming sounds. Machines with multiple gears may not make any weird sounds at high RPM, but will at a lower RPM in low gear.

The best way to test a machine is to run a part on it. Have it do rapid moves in all directions and listen for any sounds in the head and ways. Have them do other cycles, such as tapping, drilling, and some hard cuts with an end mill. These tests will give you a good idea if anything needs to be replaced right away.

Shipping

Last, but not least, do you have a way to transport or ship the machine you want to buy? CNC Milling machines are very large, and can cost a lot to ship to your house/shop if they’re out of state. Do so research and find a good company that will ship it without breaking the bank.

To get an idea of how much a machine will cost, check out some listings on eBay. That will give you a better idea on what size, age, and powerful of a milling machine you can afford.