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MachinistBlog.com

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

How I tram my mini-mill

This is how I tram my mini-mill.  I think the method I use is fairly common, although I may use slightly different equipment than others.  There are other ways of doing it and some people have strong opinions about which way is best.  I’ve included links at the bottom to some interesting discussions I found if you would like to learn more.  If you don’t know, tramming is the process of adjusting the mill’s column so the spindle is perpendicular to the table.

By the way, this procedure only trams the X-axis.  Unlike most other mills, the mini-mill’s Y-axis is not adjustable, although there are ways of doing it if you’re willing to go to the trouble.

My Equipment

  • A matched pair of 1-2-3 blocks
  • A digital dial indicator
  • The fine-adjustment arm from an inexpensive magnetic base for a dial indicator held in a 5/8-inch cross-drilled piece of drill rod mounted in a collet

I started using the arm from a magnetic base because it was the quickest and easiest way to mount a dial indicator so I could read it from the sides of the mill.  It replaced a home-made one that had the DI facing forward (good) and to rear (hard to read).

If your mill vise is big enough you can measure on the top of it with a dial test indicator (DTI) and tram your mill that way.  The vise shown in the picture is probably big enough to do that.  But the screwless precision vise I often use isn’t, which is why I use the 1-2-3 blocks, a trick I learned from someone else.  The blocks will also allow you to tram your mill without removing the vise.  I also believe you can get better results by taking your measurements farther apart.

For Best Results

Before you get started you should swing your indicator from one side to the other a few times to make certain you get repeatable measurements and there is no “play” in your setup.  You should also center your table under the spindle and make your measurements on its center line and at the same spots each time.

You should know that tramming your mill’s table does not guarantee your vise will hold your work pieces square with the spindle.  It should if it was made properly.  If it doesn’t you should find a way to fix it, consider getting another one or tram your vise instead of the table.  I’m talking about your vise being square with spindle, not with the table.  That’s also important, but it’s different topic.

One way to check your vise is to tram your table, mount a long parallel in it, and then measure at the ends of the parallel with your indicator.  It should be just as perpendicular to the spindle as your table, or pretty darn close.

It’s Easier with a Digital Dial Indicator

In the past I’ve always trammed my mill using a traditional dial indicator with a needle and dial.  Sometimes it would take me just 2 or 3 minutes but other times I’d be scratching my head for 10 or 15 minutes and wondering what the heck I was doing wrong.  It was usually because I’d gotten confused reading my “analog” indicator, which is easy is for me because as an amateur machinist I don’t use one very often.  So the last time that happened I took my old indicator off and replaced it with the new digital dial indicator I’d bought from Harbor Freight for about $25 (with a 20% off coupon).  It instantly put an end to my confusion.

The Procedure

The procedure is simple with a digital indicator.  Swing your indicator to one side and zero it.  Then swing it to the other side.  If the measurement is “negative” then push the column toward that side half the distance shown on the indicator.  If your measurement  is “positive” then push the column away from that side half the distance shown.  Then zero the indicator again and swing it to the other side to check your work.  You want to try to get the same distance on each side,  although I wouldn’t worry too much if you’re only off a thousandth or so over a good distance (my setup takes measurements about 10-inches apart).

If your indicator has a needle, then use it to find out which side has the shortest distance between the indicator and the table, and then “zero” it or write down the measurement.  Then swing it to the other side, calculate the difference in length and push the column toward that side half that distance.

Before you can adjust the column you’ll obviously have to loosen the big nut on the back of it a little.  There’s a good chance that the column will move slightly when you tighten it again, so re-check the tram.  I’ve found you can minimize that if you loosen the nut just enough to allow you to move the column by gently tapping it with a rubber mallet.

More information

CraftKB: How to tram a Sieg X2 mini mill

Practical Machinist Forum: How to tram a mill for best surface finish / flatness?

CNC: Automatically find edges, hole centers and more with Mach 3

This article describes how you can use Mach 3, the popular CNC controller software, to automatically

  • Find the edges of your work piece (and therefore the corners)
  • Find the centers of holes and their diameter
  • Set your cutting tool at a known height above your work piece or table

What’s involved

This feature is very easy to implement and use and it will cost you almost nothing.  You don’t even need a licensed copy of Mach 3.  Here’s what you’ll need to do:

  • Download and install a free screenset for Mach 3 that has the buttons you’ll need to operate these features.  There are a number you can choose from.  Keep reading to find some of them.
  • Connect a wire to an unused input on your CNC controller board.  This is the circuit board your steppers motors are hooked up to.  You probably have a spare input unless you’ve used them all up for home or limit switches.  If so there is probably an inexpensive way to add more.  You may also have to add an inexpensive and easy-to-find capacitor if have a problem with electrical “noise.”  I didn’t have to.
  • Go into Mach 3 configuration menu for ports and pins and enable the “probe” and assign the pin you hooked your wire up to.  You might have to also change the “active low” setting from its default but that’s easy to determine and do.
  • Connect the other end of your wire to a touch plate.  If you’re working with wood or other non-conductive materials you’ll just need a flat straight piece of metal for finding edges.  There’s at least a few different kinds of probes and touch plates you can use to find the center of holes and their diameters.  One is simply a short straight piece of metal rod mounted in your spindle.  If you’re working with metal then your touch plate or probe will need to be electrically insulated from your work piece.  So it will require a little more effort to make one.

It took me only about 40 minutes to get it working on my mill, although that doesn’t include all the research I did first.  I also made a quick-and-dirty touch plate and I still need to make a couple of better ones.  I’ll be writing more about that later.

More details

“Erniebro” on CNCZone didn’t come up with the idea for an auto edge finder, but he deserves an enormous amount of thanks for publicizing this method and making it easy for others to start using it.  He designed the first screenset for adding this feature to Mach 3, made the video above, posted excellent instructions on CNCZone describing how to install it and patiently provided help and support for those who needed it.  Others have built upon his work and made improvements, but if you want to try this I suggest you start with ErnieBro’s instructions.

  • One of the first things you’re going to want to do is download Erniebro’s Mach 3 screenset.  I just want to let you know that if you’re NOT a registered member of CNCZone and logged in, you’ll get an error message that might make you think the file is no longer available.
  • There’s a very good chance you won’t have any problems getting your machine to work properly.  If you do there’s also a very good chance that someone else has had the same problem and you’ll find the solution in Erniebro’s forum thread.  Unfortunately, the thread has grown to almost 400 posts and it takes a lot of time to read them all (trust me, I’ve done it).  So I suggest you take advantage of the “Search this thread” link you’ll find near the top of each page, just above the messages on it. You’ll need to be logged in to use it.

How to use a digital caliper (and more)

 

A couple of Harbor Freight digital calipers and a long-lasting SR44 battery. The top one costs a little more but it can also display fractions. More importantly, it has a bigger and brighter LCD display and it works a little smoother.

 

Shortly after I started MachinistBlog I wrote about a couple of good web sites that can teach you how to read a micrometer.  That post has been surprising popular.  So now I want to tell you about this excellent web page that might teach you some things about using a digital caliper that you don’t know.

Harbor Freight Digital Calipers

Unfortunately, my budget hasn’t allowed me to invest in a nice $145 Mitutoyo digital caliper like the one shown in the tutorial.  I’m still using Harbor Freight digital calipers that you can buy on sale for about $20 or less.  My first was HF’s least expensive 6-inch stainless steel digital caliper, which I think you can still find on sale occasionally for about $10.  It still works well, although I did manage to break the tab that holds the battery cover on.  Black electrical tape now does that job.

About a year later I bought a slightly more expensive 6-inch HF digital caliper that could also display in fractions of an inch.  I found that feature to be pretty useless but its slide works much smoother and I really like its bigger LCD display.  I haven’t seen this caliper (#98851)  in my local Harbor Freight store in a while and it also recently disappeared from their web site where it used to sell for about $25.  I’ve been using mine for about 3 years now without any problems, although it doesn’t get the amount of use a professional machinist would give it.  I have verified its accuracy with a very good set of gage blocks, although I haven’t done it in awhile.

I didn’t know this until just now, when I was looking at HF’s web site, but their digital calipers have a lifetime warranty.

Battery Life

The battery in the Mitutoyo caliper is supposed to last at least 3.5 years.  The batteries in Harbor Freight calipers seem to last somewhere between 2 months and a year.  Many don’t seem to know this, but you can use either LR44 or SR44 batteries in them.  They come with LR44s, probably because they’re cheap.  You can sometimes buy 10 for a $1, but they don’t last very long because they have a lower voltage output.   The SR44s are silver oxide batteries and they produce a higher voltage and store more energy.  So they’ll last a lot longer before their voltage drops below what your caliper needs to operate.

I haven’t tried any name brand SR44 batteries yet so I don’t know what they cost or if they’re much better than the ones HF sells for 99 cents.  You can either buy the cheap LR44s and constantly change your batteries, or you can buy the more expensive SR44s and change them maybe once or twice a year.

Your Opinion?

I’ve never had a chance to use an expensive digital caliper so I can’t compare my HF calipers to one.  I’d love to know your opinion if you’ve used both, or if you have other knowledge about digital calipers that you would be willing to share with us.

Making Particle Board Workbench Tops

This article describes how I make workbench tops using particle board.  I’ve been using this method for about 20 years with good results.  Although the next time I build a similar bench I may use a laminate counter top for two reasons, which I’ll explain later.

I don’t like benches that move, shake or vibrate.  I think the heavier the frame and top are the more stable a workbench will be and the better it will dampen vibrations.  Particle board is very heavy which is why I like to use it.  To make it even heavier and stiffer I glue two 3/4-inch layers together.  Particle board is also very dense, unlike plywood and MDF,  which means it won’t dent very easily or much if you hit it with a hammer or drop something heavy on it.  It’s also inexpensive and it won’t warp.

I’ve tried using plywood but it dented and splintered easily.  Wood planks will do the same.  Plus planks can warp and it’s not easy to build a smooth seamless work surface out of them.

Construction

I built the L-shaped bench shown in the picture a couple of years ago.  The frame was built with 2x6s instead of 2x4s to make it strong enough so I could eliminate all but two legs and keep the space under the bench unobstructed for storage.  The legs are at the ends and are made from pressure treated 4x4s.  I began construction by screwing the back rails to the wall studs.  I made certain they were level and used screws that could support a lot of weight.  Then the front rails, side rails, legs and cross braces were added.  I used metal joist hangers, angle brackets and deck hardware to fasten them all together.  They added to the cost but I think they made the bench much stronger and quicker to build.

You might want to bring some help with you when buy the particle board because 4×8- foot sheets are heavy.  I got Home Depot to rip them in half lengthwise.  It saved me a lot of work and made the boards easier to handle to bring home.  If you have them do it make certain they measure correctly.  The first sheet they cut was off by 3/4-inch and I wouldn’t accept it.  They very graciously cut another.

This L-shaped bench top was harder and more complicated to make than a simple rectangular one.  I began by fitting the lower-layer pieces against the walls.  Then I cut and glued just one of the top pieces so it overlapped the seam in the bottom layer. When the glue was dry I fitted and glued the remaining piece, making certain that it butted very tightly against the other one.  I also made certain it was well clamped and weighted down while the glue dried.  I ended up with a very tight seam that only needed a little bit of wood putty to make it disappear completely.  It’s still invisible two years later.

I used the “original” Gorilla Glue to glue the particle boards together.  There might be cheaper alternatives but I wasn’t going to take any chances on the seam between the two layers coming apart.  This kind of Gorilla Glue is water activated and you’ll need to use a spray bottle or wet rag to slightly dampen the surfaces just before you apply it.  I used a plastic spreader to spread it out evenly.  Then I used lots of clamps along the edges to make certain I got a good bond with no gaps.  I also stacked as many heavy objects as I could on the rest of the bench to weigh it down.

It’s not likely that you are going to get both layers of particle board cut and lined up so the edges are perfectly even.  So after all the glue was dry I used a router with a flush cut bit to make them even.  This may require positioning your router on both sides of the bench top.  I couldn’t do that because there wasn’t room to flip my L-shaped top upside down, and the support frame prevented me from holding the router upside down against the edge.  So I had to plan ahead and make certain that the top layer extended beyond the bottom one a little bit so the router bit could trim it flush.

I then used the router with a 1/2-inch round-over bit to round the edges of the workbench.  It’s a little bit more work, but I think it makes the bench top look more finished and professional looking and it makes the edges more comfortable to lean against.  Rounded edges also won’t dent or splinter like sharp ones will if they get bumped with something heavy or sharp.  They’re not hard to make but I recommend practicing on scrap first. Continue reading Making Particle Board Workbench Tops

Random Quote

Whenever you have an efficient government you have a dictatorship.

— Harry S. Truman