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MachinistBlog.com

Plans, projects and how-to's for home machinists

Inexpensive DIY tachometer for a mill or lathe

It looks like Adam mounted the sensor in the spindle cap and is using putty to hold the magnet on the spindle. I would have done it a little differently.

Here’s an idea I haven’t seen before.  Adam made a very inexpensive tachometer for his variable speed X2 mini-mill using a cyclometer (bicycle speedometer).  Almost any wired cyclometer will work and you should be able find one with a nice big display for less than $15.  (You probably don’t want to get one that has a wireless sensor because they’re more expensive, you’ll have an extra battery to replace occasionally and you might get erroneous readings caused by the receiver picking up electrical noise from your motor).

Someone left a comment with a link to a tutorial on Instructables with more details about making one of these.  The author, Jose, explains that you basically just have to glue the magnet that comes with the cyclometer to your spindle and somehow mount the sensor within about a 1/4-inch of the magnet when it spins around.

The sensor sends a signal to the cyclometer every time the magnet goes by it.  The cyclometer uses that information to calculate the bike’s speed using the wheel’s circumference, which you have to tell it.  In this case though, we don’t want to know speed, but RPM instead.  Jose says to use 268 mm for the wheel circumference if the cyclometer displays the bike’s speed in MPH, and 167 mm if it displays in KPH.

He says those numbers will display the RPM in hundreds, regardless of circumference of the object you mounted the magnet on.  I don’t why that is, even though I was once good enough at math to get an A in college calculus III.  There’s a chance I’ll wake up in the middle of the night with the answer, or have a revelation while in the bathroom.  But just in case I don’t, I would appreciate it if you would leave a comment with the answer if you have a good “explanation for dummies.”

A Homemade DRO for the 7x Mini-Lathe

The DRO uses an inexpensive digital dial indicator that’s held in place on the apron with powerful rare-earth magents. The stop clamps to the top of the cross-slide and presses against the indicator’s plunger, which measures the movement of the cutting bit.

This article describes how I added an easy-to-make DRO (Digital Readout) to the cross-slide of my 7×12 mini-lathe.  It uses an inexpensive digital dial indicator that I bought from Harbor Freight for about $25.  It works very well and you won’t have to drill any holes in your lathe or disassemble it to install it.

I’ve rarely seen a picture of a mini-lathe with a home-made DRO on it (or any kind of DRO), even though they seem to be fairly common on mini-mills.  The ones for mills are usually made from inexpensive digital calipers or scales.  I considered using them on the mini-lathe but rejected the idea because there is very little room to put them where they won’t be in the way.  They will probably collect piles of swarf, the displays are also likely to be difficult to read and the buttons will probably be located where they will be awkward to push.

Using a digital dial indicator eliminates or minimizes those problems, although it is not a perfect solution.  You’ll have to read the display and buttons upside down, which is not really much of a problem because they’re quite large and easy to read.

The indicator has a range of just 1-inch, but my design uses an adjustable bracket that will let you engage the DRO where ever you need it.

The DRO has two parts.  The first is the indicator holder.  It’s an aluminum bracket that attaches the dial indicator to the apron using very powerful rare-earth magnets.  The magnets are located where they are unlikely to attract steel or iron chips.  The second is a stop that clamps to the top of cross-slide and makes contact with the point of the indicator.

The stop can adjust two ways so it can always be made to press against the indicator’s probe, no matter the diameter of your work piece.  You just slide it along the top of the cross-slide until it makes contact with the tip of the indicator, which is mounted on the apron.  I thought there might be situations, like when working on a very large diameter workpiece, where the stop might not be able to contact the indicator.  So I also added an adjustable rod to extend its reach.  I now know it’s not needed, although it might if you adapt my design to another lathe.

The DRO does not interfere with the lathe’s controls and you can easily remove it in seconds if you want.

The DRO works very well and it has really improved my productivity.  I no longer have to keep stopping to measure how much more metal I have to remove, or keep track of how much I’ve turned the cross-slide knob and  then calculate how much more I need to cut.

Most of the time the DRO and the cross-slide dial are in complete agreement, or at least within five ten-thousandths (.0005), which is the resolution of the DI.  When they disagree it’s usually because of backlash.

However, I was surprised to find that they would sometimes consistently disagree by forty-five thousandths, and it wasn’t due to backlash.  I haven’t fully investigated the cause yet, but I’m pretty sure it’s going to turn out to be axial end play in the leadscrew.  It’s a pretty common mini-lathe problem caused by a gap between the head of the leadscrew and the flange it is suppose to turn against.  The most common fix is to make a small washer to fill that gap.  It’s not really an issue and I’ve learned to trust the DRO.

Construction

This a prototype and not a finished design.  I am hoping that others who are smarter and have better machining skills will think of ways to improve it and then share their ideas.  That’s why there are no plans for it yet (a shortage of spare time and poor CAD skills also has something to do with it).  So, until I get some plans drawn, I hope my photographs will allow you to make your own if you want to.  Please let me know if you have any questions and I’ll do my best to answer them.

Continue reading A Homemade DRO for the 7x Mini-Lathe

Free Plans: Quick-Release Lathe Mounted Dial Indicator Holder

QRHLD1SwarfRat Enterprises has a set of free plans for a quick-release dial indicator holder that mounts on the front of a mini-lathe.   The holder is made from a 5-inch long piece of .875-inch square aluminum stock.  It also uses a quick-release lever from a bicycle seat or wheel that can be purchased inexpensively or salvaged off an old bike.  It looks like it should be fairly easy to make, although it will require a mill.

I am thinking about making one but not to use with a dial indicator.  With a little modification it might make a great carriage stop, much better than the one I’m using now.  For those rare times when I need to measure the movement of the carriage I use a dial indicator with a large magnet mounted on its back.  It’s easier to make and I can also use it on my mill, which makes it a really useful tool.

SwarfRat also makes instructional videos that will show you how to use a mini-mill or mini-lathe, how to repair them, and how to use some tooling like a rotary table.

You can buy them at their web site.  SwarfRat also rents them for about $9 a week.  That seems like a pretty smart move because there’s another company becoming well known for the how-to videos they specialize in renting.  That company probably buys just one or two copies and keeps renting them out.  My guess is that all those rentals destroy the sales of the companies that invested time and money to produce the videos and removes the incentive to make more videos we might be interested in.

But for some strange reason SwarfRat does not rent all of their titles, only a few of them.  And I’m disappointed because they don’t rent their video about the rotary table, which is the one I would really like to see because I just bought one.  They also don’t provide any sample videos and I can’t find any reviews of their products.  So I’m not going to be taking a chance and spending $44 to buy a copy.

Lever-Operated Tailstock Cam Locks – Three Well Known Designs you Can Build and a Kit you Can Buy

It has been more than a year and a half since I bought my 7×12 mini-lathe and I finally decided I needed to get serious about building or buying a cam-operated tailstock lock for it. A lever-operated lock is probably one of the most popular modifications for the mini-lathe because it increases your productivity by eliminating the need to find a wrench and turn a nut every time you want to move the tailstock.

Much of my delay has been because of my indecision about which of the various designs floating around the Internet is the best.  So I started sorting through my collection of bookmarks and found that I needed to compare three well-known designs I could make, plus a kit I could buy and install easily.  Continue reading Lever-Operated Tailstock Cam Locks – Three Well Known Designs you Can Build and a Kit you Can Buy

Random Quote

The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt.

— Bertrand Russell