Tag Archives: machining

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.

 

2 vs. 3 Axis Machining – CNC Profiling

Traditional 2-axis milling on a CNC machine is still very common, you adding another axis to the equation greatly expands your possibilities. You can make parts that you might not have been able to before when just using 2-axis programming, and it can possibly reduce cycle times.

First, we must establish the difference between two and three axis machining. Most CNC mills these days should be able to accept and perform programs with 3-axis machining. Two and three axis machines both have an X, Y, and Z axis, but using that third axis for milling profiles can allow you to profile the surface of a part.

In 2-axis milling, you can move in the X and Y-axis at the same time if you’re milling the outside or inside profile of a part. If you’re using the third axis, you can make X and Z-axis moves while milling a profile, such as a waving contour. You can also move in the Y and Z-axis if you simply change the plane that you program in.2 vs. 3 Axis Machining - CNC Profiling

If you’re hand-writing the program, G17, G18, and G19 are the CNC commands for selecting which plane you want to machine on.

G17 is the XY plane.

G18 is the XZ plane.

G19 is the YZ plane.

Other than that, programming is virtually the same as any other G-code program. If you want to make a positive Z and negative Y move, an example would be:

G90 G20 G19 (To set the YZ plane and absolute)

 

G1 Y-.5 Z2.23

If you want to go back to the traditional XY plane, a line with G17 will be needed.

If you have rendering software or a program that simulates your program, I strongly recommend using it on a new program, especially if this full 3-axis machining is new to you. Good luck, and go experiment! The best is experience is with machine time and trying new things.

What Is Lean Manufacturing?

Any company in the machining industry has to incorporate Lean Manufacturing in their business and process plan to survive these days. To put it in simple terms, lean manufacturing is the production practice of being efficient by eliminating any ‘waste’ in the process plan. Though they may not call it this, all companies strive to be lean because it makes their customers happy, and ultimately, more money.

Although there was seven original “Wastes” involved in lean manufacturing, we’ll look at eight of the most common ones in a machine shop. Most of them are simple, but it can take a lot of work and orchestrating to implement them all. There is no perfect company that has it all figured out. There is always room for improvement, which is why employers seek new ways to lean out their manufacturing process. The acronym for this practice is “DOWNTIME”. Now you could just look this term up on wikipedia, but it won’t give you a real perspective or example of what it means. Those are just general illustrations in the manufacturing industry, but working in a machine shop may produce different scenarios.

Defective Production:

If bad parts are made, it takes more time to either re-work it or make another one. More material, more machine time, more tooling wear, which can add up to almost double the cost of a part. The machine shop pays for this and not the customer, and that is why it is on the list of big “wastes” that companies try to eliminate. We are only human, so mistakes do happen occasionally, but the goal is to decrease the percent of defective parts.

Overproduction:

I believe that this one can go either way, but if space is expensive, then overproduction is definitely considered a waste. If you make extra parts for a customer, it costs more time to make them, and the excess supply of parts costs more to store because it takes up more space in between machining and shipping, plus the time it will take for the customer to order more. If something happens to the customer and they discontinued that part or went to a different vendor, your extra inventory has now turned into a complete waste of money.

Waiting:

There’s two ways you can look at this; the parts that are waiting, or the machinist that is waiting. This happens whenever you have stock waiting to be cut or for operations on a machine. There is usually a waiting time in between finishing the parts and shipping. This takes up valuable time, as well as space. Although it may not seem like a big difference if parts are waiting an extra day or two to be worked on or shipped, the quicker you get the parts out your door, the quicker you can move on to another part/order.

Non-used Employee Talent:What Is Lean Manufacturing

This should be an easy, but too many employers miss it. If you have an employee that is skilled multi-axis machining and/or programming, putting them on a grinder or running simple mill parts is a waste of talent. Even if they need a little more training, it’s much more efficient to move that employee to the more complicated work instead of hiring another person, which you may have to train-in anyway.

Transportation:

Transportation is all of the unneeded movements of parts and materials. The shortest route from point A to point B is a straight line, anything else is wasting time. While it’s not always possible to do this in a machine shop, the shorter the distance parts and material have to travel the better.

Inventory:

This is similar to overproduction because having too big of an inventory takes up space and takes more machine time to run. If you’re making more parts than the order requires, it is considered wasteful inventory.

Motion:

Much like wasteful transportation of parts, a machinist should reduce wasteful motion as much as possible to be efficient. If you’re setting up a job, all the tools should be set-up and ready to go or on the workbench next to the machine. This can be done during cycle time of the previous job to save time. When loading and unloading parts in the machine during production, as well as part deburring, having everything close by or within reaching distance will reduce motion and save time in the long run.

Excessive Processing:

Like mentioned before, time is the biggest money breaker or maker, and if you’re spending too much time trying to perfect parts or orders when it is not needed, then you’re wasting time. If you have wide open tolerances on some or most of the part features, spending extra set-up and/or cycle time to try and get it right at the nominal number is waste. As long as all of the parts are within tolerance of the blueprint, they’re good. If the part doesn’t go together during assembly or function properly, it’s that customer’s job to fix the print, not the machine shop’s job.

Now, how can YOU as a Machinist benefit from all of this? This can help boost your reputation at your current job, as well as your resume. The harder you work at being more efficient, the more your boss/foreman will notice. This may result in better raises, a promotion, or benefits in various ways.

Although not all of these factors directly relate to you, suggesting them to higher authority may give you better recognition in the long run.

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.

Machinist Square – What Shape Are Your Parts?

If you’re a new or home machinist, learning how to “square your parts” is one of the first things you should learn. There’s quite a few common tools that a machinist should have in their toolbox, and a Machinist Square is one of them.

Learning how to machine a part on a manual milling machine should be one of the first things in school. Eventually you will need to make parts with tighter tolerances, and flatness/perpendicularity are a big part of it. If your parts are trapezoidal because of tool deflection, I can guarantee that your parts will be rejected.

Machinist Square Set
Machinist Square Set

A good machinist square should be perpendicular/flat within .0002″ tolerance, and should be periodically calibrated so that it stays within spec. However, some squares have a different rating that depends on how accurate they are. A & B are the most common, with B being for the average consumer that doesn’t need extremely close tolerance parts.

A is the higher grade, and while it will cost more, it is what you will want for machining. Don’t skimp out and get the cheapest one you can find. You get what you pay for, and in CNC manufacturing these days, you want every advantage possible.

If you drop it and can see a dent or bend in it, it’s worthless. That’s why it’s critical that you take care of not only a machinist square, but all of your machining tools.

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