Category Archives: Tips

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.

Machinist Toolbox – What To Buy?

Are you new to the Machining industry or considering a career in this field of manufacturing? A toolbox is one of the first things that you should buy. It’s where you will keep most if not all of your tools, personal inspection equipment, and books/manuals such as the Machinery’s handbook.

Kennedy tool boxes are well known in the Machining industry because they are well built and have been around for 100 years now. If you’re looking for a tool box that is made in the U.S.A., a Kennedy is the way to go for a new Machinist, whether it’s a top box, or a bottom as well. These boxes are made specifically for Machinists, so the length, width, and depth of each drawer is designed for specific tools, allowing you to easily organize your set-up; and we all know that time is money when running CNC machines.

Kennedy Top Box
Kennedy Top Box

If you’re on a budget, a standard tool box can work just about as well. It may not be built to hold your machining tools as well, but you can find good deals on sturdy boxes that will save you money for buying even more tools!

There are also some Machinist knock-off tool boxes are on Amazon for a fraction of the cost, such as this 11 Drawer Roller Box. Due to its low price, it won’t have the same quality as say a Kennedy, but some of the same features are there with a similar layout. Like most anything these days, you generally get what you pay for. For something such as a tool box, if you’re a rookie machinist, then a cheap box may work just fine.

What To Look For?

If you are just starting your CNC Machinist classes at the local Tech school and had to buy a tool box without doing any research then it probably won’t make much difference at first. After going to school or working for some time, though you’ll realize what you want in a tool box, and even that may change after being on the job for years.

Size is the biggest factor when purchasing a new tool box. Obviously if space is unlimited and you don’t plan on transporting it often or ever, then the bigger the better. If you buy a big box right away then you won’t have to upgrade right after buying a handful of new tools. On the flip side, if you don’t have many tools then you’ll be pushing around a lot of dead weight if you move around the shop on a weekly or daily basis.

If you have a chance to look at and test out tool boxes in person, I would suggest looking at and opening the drawers to see how smooth they are. Ball-bearing drawers slide out nicely compared to the conventional slides. This feature isn’t necessarily a deal breaker, but it’s always nice to have things that perform better.

Castors are the wheels used on tool boxes and are another feature that should be considered when doing research. Putting a lot of heavy tools in your box will put more strain on the castors, so it’s good to have big and sturdy castors.

If you still can’t figure out which one to buy, there’s nothing wrong with having one, two, or three boxes to choose from.

A quick tip on how to prevent tools from getting nicked and scratched up after constant opening and closing of drawers; tape a sheet of felt or lay a thin rubber mat down in each drawer for padding and to help prevent everything from sliding around.

Tool Runout vs. Tool Deflection – What Are The Differences?

There’s a reason tight tolerance parts cost more time. Yes, I use the word “Cost” because time is money, and it can take a considerable more time to set-up and run a part if the tolerances are closed up. Tool run-out and tool deflection can both be an issue when trying to hold a close tolerance. However, they are not the same thing.

Run-out

Tool run-out is how far off of the rotating axis the tool is. While in the machine, you want to check just above the bottom of the tool, as that will give you the most accurate reading and is almost always worse than the top of the tool where it goes in the holder. To check it, put an indicator on a vice and touch the tool off of it. Zero it out and then rotate the tool (usually in a counter-clockwise rotation so it doesn’t catch the cutting edge). If there’s run-out, one side of the tool will give you a different reading on the indicator.

Before we go any further, let me explain what run-out actually does when machining a part with a tool that has it. If an end mill or a drill has excessive run-out, the side (or flute) that is bigger will do more cutting. If you’re milling out a hole with an end mill, it will cause the hole to go over-size if all of your program and offset numbers are right. A drill can also go oversize, as well as drill an oblong hole.

Now lets take a look at what causes a tool to have run-out. A brand new and unused tool can have run-out. Why? Not all tools are made the same, and if you buy cheap tooling, there’s a better chance that it was made with the same precision as a higher quality tool.

Not only can the tool be at fault, but a defective tool holder can cause run-out as well. On the other hand, you may check the tool while in the spindle and see that their is run-out, but certain tools (such as a reamer or drill) will allow you to slightly move it without removing it. This can often get rid of many run-out problems with longer tools.

Tool Deflection

Tool deflection should not be confused with run-out. It is a common term used when side milling with an end mill, and it causes a taper in the part feature that is being milled.

Take this as an example; you’re milling the outside profile of a part (2x2x2.25″) that has blueprint dimensions of 1.950″ wide, long, and 2.000″ tall. Using a 3/4″ end mill with greater than 2 inches of flute length, you mill around the part once. The top of the part is 1.951 all the way around, but the bottom is upwards of 1.954″. This is because the end mill is too long and was ‘deflecting’ because it couldn’t handle the pressure of removing all of that material.

That’s the most simplistic scenario of tool deflection. So, how do I combat this? Great question, and there’s quite a few ways to make sure your part is square, perpendicular, and/or parallel.

First of all, how deep of a cut are you taking? If you’re drilling a 1/4″ hole that’s .375″ thru, you don’t need a jobber drill with 4″ of flute length. When milling, a bigger diameter tool will be stronger and resist deflection better. If you’re milling a feature that is .400″ deep, using an end mill with 1/2″ flute length will achieve the best results. One last thing on tool length is that you should have the tool as short as possible in the holder. Do not clamp on the flutes, but if you choke up on the tool, this will also help prevent deflection.

Feeds and speeds. I’ve said it before, and I’ll continue to say it. Having the right RPM and feedrate for your tools is one of the major keys to success in the Machining industry. Even if the surface foot is close, having a high feedrate will naturally produce more tool pressure and in turn cause deflection.

Slowing down the feedrate can help, but in the end, you may have to take multiple passes to make a feature square, especially if you’re profiling out a part with an end mill.

 

Drill, Bore, Ream, Oh Why!?

Drilling, boring, then reaming is the proper order of operation when machining a hole. This is just one of the fundamentals you will learn in Machining 101. Whether you’re on a manual mill or a cnc milling center, this process will get you the most accurate hole size.

Why can’t I just drill? That is a very good question, if you’re just starting out as a machinist or are in training, you probably won’t know how every kind of tool is going to perform. While a drill, even when spot drilled, can make a nice looking hole, it can’t always hole a tight diameter or circularity tolerance. A standard drill can walk, and that can change the location if it’s a thru-hole. Drills are not always ground perfect, resulting in one lip bigger than the other. This causes the hole to be more egg-shaped and often over-sized.

Want a perfectly circular hole? The boring bar comes next because, unlike a drill, it is sturdy and will follow the same path all the way down the hole. A drill is floating in its holder that causes run-out, but a boring bar is sturdy and will make a circular hole, whether the existing hole is already or not.

Boring Bar and Inserts
Boring Bar and Inserts

The reamer comes last if you want an accurate hole. You should only leave several thousandths left after boring, depending on what material you’re cutting. A reamer is much more precise than a drill, but it will follow the path of the existing hole. This is why you should bore the hole prior to reaming, otherwise the ream will follow the path of the drilled hole, which may not be straight. A bore is accurate, but you can get a better finish with a reamer, and it can still hold tenths for a tolerance if you have a good reamer.

How To Read A Part Blueprint For CNC Machinists

Reading a blueprint accurately is extremely important in the machining industry. If you can’t decipher a print or flip your views (more on that later), you’ll have a hard time meeting the part requirements.

The first thing to look at is the job description box. It has all of the material, part number, revision, date, and other information about the part. If you’re just an operator or a set-up guy, the most important things are the material and part number, as well as the tolerances if given. Always check to see if there are revisions, however, in case the program needs to be modified to meet the new dimensions/tolerances.

If you’re on a milling, look at the overall length of the part. If it’s square or rectangular, how wide is it, and what is the height? What are the tolerances? If there’s no specified, there’s generally a set tolerance in the description box that depends on how many decimal places the dimension is. So, if the part is 4.75″ long, and the tolerance for .xx decimal numbers is .01, then the tolerance is 4.750″ + or – .010″.

If there’s any milling features involved, you’ll need to check the length, depth, width, and possibly angles of them too. Calipers, micrometers, and depth mics are good tools to check dimensions quickly, but if you need to check something that has a very tight tolerance, more expensive tools or machines are required.

Basic Part Blueprint
Basic Part Blueprint

Holes are pretty straight forward. They can be drilled, bored, reamed, and even circulated-interpolated by an end mill. Look at the blueprint to see if the specified hole is a through or blind hole with a called out depth. If it has a given depth, does it need to be a flat bottom, or can it be left with a drill bottom? If a hole has a tolerance of .002″ or less, ground gauge pins should be used. Large holes can be checked with more expensive tools, depending on what your machine shop has.

Counter-bores and counter-sinks are usually machined in relation to holes. A counter-bore will have dimensions for the diameter and depth of the bore. A counter-sink will have diameter dimension, as well as a given angle. Not all counter-sinks called out are 90 degrees, so always pay close attention.

Another common feature to look for is threaded holes. They can be tapped or cut with a thread mill. Nothing too special about threads either, just check the minor diameter with go and no-go gauge pins, as well as the major diameter of the thread with thread gauges. Your shop should have a collection of thread gauges of all common thread sizes and pitches, as well as any specialty thread required by a customer.

Are there any radius features on the part blueprint? A radius can with be milled by and end mill, or cut with a radius tool cutter. If you are running a part that has been made in the past, then you shouldn’t have to adjust the tool or radius offset much, if at all. The radius should make a perfect blend with the flats. Check it with a radius gauge or optical comparator.

A chamfer is often used on the edges of a part as a part of deburring and to make the part look much cleaner and more professional. It is a simple call-out on the print, as you only need to check the size and angle of the chamfer. If you have a large amount of tolerance, you can check it with a depth micrometer.

Also, hole or feature dimensions are very critical. They will usually come from the origin or the edge of the part. Dimensions often come from part features as well. Such as if there’s a line of several holes, the first hole dimension will come from the part edge. then the second hole dimension will come from the location of the first hole, and so on and so forth.

In reality, reading a blueprint isn’t all that difficult, it’s basically just a lot of common sense, and memorizing certain manufacturing symbols. Don’t be intimidated by a print with lots of numbers and detail, just take your time and read everything carefully. In fact, I would rather have a part blueprint with too much information than too little, although having the print cluttered with extra numbers is not efficient.

Basic Machining Tools – Terminology

There are a lot of tools used in machining today, so it’s often hard to keep up with the names of all of them, especially if you’re new to this career. Every tool has a specific job, and while a variety of tools may be able to get the job done, some are better than others.

Just so I don’t overload you, I’ll go through a list of the most common tools used in Machine shops, as well as Machine Tech schools. Each tool has a specific purpose, and there are many different kinds of the same tool. The more tools you use, the more knowledge you will get and know what works better for a certain material or operation. However, you must get an understanding of the of machining tools before just using any specific one without knowing what it’s meant to do.

End Mill

The almighty ‘End Mill’ is one tool that you will use almost every day if you run milling machines. If you need to cut both ends of a part to get it to a certain length, and end mill will side-mill the ends to make a clean and parallel surface. It can cut out pockets, and make square or round features in a part. There is so much that you can do with an end mill on a CNC milling center.

3-Flute End Mill
3-Flute End Mill

Whether you need to rough out a large solid piece of steel, or you’re just making some finish passes on aluminum, there’s an end mill for each job and every one in between. There are many different kinds of end mills. Here are the main variables you will have to decide when ordering tools: size (diamter), length (flute length), material/coating, roughing/finishing, number of flutes, and more.

Drill

Need to drill a hole? How about a few hundred holes? While there may not be quite the selection for drills as end mills due to the fact that you can only do so much with them, there are definitely right and wrong drills for any given job. 118 degree HSS or coated drills are the most common since they work well with most basic materials. However, you may need a drill for a hard stainless job, or perhaps a copper part that requires a deep hole with a close tolerance.

 

Tap

There’s not much else you can do with a tap other than tapping holes. Are you doing a blind or a thru-hole? Is it a metric or a U.S. standard thread? If you’re on a mill, the most popular taps are: cut tap, roll form, spiral point/flute, as well as a thread mill.

Cut taps produce chips because they literally cut a thread into the existing hole. You must use a drill that meets the minimum diameter tolerance for the specific thread you want. They are used on thru-holes because the chips won’t get in the way of the tap.

A roll form tap does not make chips because it forms and pushes the threads into place. It’s great for blind holes because the tap won’t break from chips collecting at the bottom.

Ream

A ream is used after a drill or a bore to meet a close tolerance call-out on the blueprint. Cheap drills are far from perfect and can easily make a hole over-sized, which will be rejected if it’s not within print. However, if you drill the hole .010″-.015″ under-size, you can then use the correct size ream to get a much more accurate and consider hole.

Ream
Ream

However, you should know that a ream will not ‘fix’ a hole. A ream just follows a hole, so if it’s crooked or out of round, the tool will follow that path. This is one reason why you may need to drill the hole then use a boring bar to make it perfectly round and straight before you ream it to size.

That’s it for the basic tools on this article from CNC Machinist Training. Stay tuned for another article that explains more advanced tooling that makes it much easier to do a job…

Roll Forming Taps Vs. Cutting Thread Taps On A CNC Mill

This is a question that comes up quite often for machinists new to the industry, and even experienced machinists that don’t know a lot about tapping. While form taps and cut taps can both do the same job, which is making a threaded internal hole in a part, they are quite a bit different in how they work.

After using both kind of taps for a while, you’ll see the difference in looks right away. A cut tap doesn’t have a full thread until about the third time around, while a form tap looks the same from bottom to top. A cut tap also has clearance cut around the tool so that chips will move out of the way and not break it.

Cut Tap

Tapping with cut taps has been the most popular for decades because that’s what there was available. They are easy to use; just drill the hole with the correct tap drill size, making sure you go deep enough so that the tap will get enough threads, then run the tap into the hole. Depending on your machine’s capabilities and what material you’re running, you may only be able to run it at 200-300 RPM.

Rigid tapping is a very useful option on newer CNC Mills such as a Haas. It allows you to tap at higher RPM without putting so much load on your spindle. This equates to much faster tapping cycle times.

A cutting tap is great for thru-holes, as you won’t have to dig into the hole to pull out the chips. You also won’t have to worry about running into anything unless your table or fixture is under the hole.

Since this type of tap “cuts” threads into the hole, you can get away with using various coolants and mixtures without breaking tools, especially on soft materials like aluminum.

Form Tap

Form Tap vs. Cut Tap
Form Tap vs. Cut Tap

What’s better about form taps? Well, they have several advantages over cut taps that will make you want to use them more often. For one, they don’t make any chips. A form tap does just that, it “forms” the threads in the hole with pressure, as opposed to “cutting” threads.

That brings us to the next advantage; the threads are much stronger because they are “formed” into place. If you need strong threads in your parts, form taps are the way to go.

Form taps are stronger and will last longer than cut taps. This will save you time and money in the long run, as you won’t have as many taps breaking in your parts.

Not only will everything be stronger, but you can run at faster speeds, greatly reducing cycle times.

With all of these advantages, there’s gotta be some downfall, right?! Well, due to the higher pressure on the tool and part hole, it will require some better coolant or oil with high lubricity. If your coolant isn’t good enough, the tap will be have to work harder to form the threaded hole and eventually will break.

This is especially true on small form taps such as an M3 (Metric), as there just isn’t enough space for the average coolant to lube the tap. You need something with better lubricity that will reduce the load on the tool. Also, if your countersink isn’t big enough, the first thread will be pushed up above the material’s surface and will cause interference if it’s a mating part.

Other than that, there really isn’t much else to say about form taps. Sometimes you just have to experiment until you find out what works the best. If your tap keeps breaking, change it up with different speeds, coolant, or a different tap.