Thursday , February 22 2018
Home > Mill Projects > Free Metalworking Project Plans: Adjustable Boring Head (Mill)

Free Metalworking Project Plans: Adjustable Boring Head (Mill)


Material: Steel
Units: (in)

If you’re looking for an advanced project to tackle with your Mill, this is it. Once complete you’ll have a quality boring head without spending hundreds of dollars on one!

I’m planning on machining this project next, I’ll post pictures along the way. For now, here are the plans:

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About Tyler

Tyler is a hobby machinist and 3D printing aficionado. He teaches computer programming and web development at Highline College near Seattle. Tyler founded Projects In Metal in 2008 because he was frustrated by the lack of free plans available for hobby machinists.

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  1. Has anyone tried this project yet? Its challenging and im confident mine will come out nicely.  However…I am trying to figure out how to make the 13/32 counterbore on the cylindrical piece.  Does anyone know where i could purchace an endmill long enough to be able to counterbore that hole? Or does anyone have another idea of how to make that feature?



  2. Hello there drunken_master.

    I have not done this project yet however the way i would do it is as follows. Firstly you will have to make an attachment. Find some stock of suitable size and length and in one end drill and tap the same thread as the slot drill.( I wouldnt use an end mill for this as end mills arn't designed for plunge cutting.) Once you have your tapped hole screw in the slot drill and you will now have an extension you can put into the drill chuck. Does this make sense? your basically screwing the cutter into a bit of stock and putting the bit of stock into a chuck.

  3. Hey Mad, this is a timely question because I was just watching a machining video with a buddy where the guy used a “slot drill”. My machinist buddy and I looked at each other asking “What's a slot drill?” We googled it and they look like a 2 fluted end mill. I'm wondering if we don't call them slot drills over here in America? I'm rather new to the hobby, but my friend has been a machinist for over 30 years and he'd never heard them called that before either.

    So, is there a difference between a slot drill and a 2 flute end mill?

  4. Really? I suppose thats what happens on the other side of the world! Yeah slot drills are 2 fluted endmills designed to drill straight down into the material. I think its because there is one tooth at the centre of the end face. You look at a end mill with four flutes and the centre of the end face has no cutting edge. So end mills are designed for cutting on there sides and slot drills for plunging…? Does this make sense? haha. Im finding it hard to describe!

  5. Hi,

    The slot drill / end mill terminology is regional:

    In the USA the terms “end mill” and “centre cutting end mill” are used.  In the Uk we use the term “slot drill” for the centre cutting tool.  A slot drill has only two (sometimes three) flutes while the endmill has four or more.

    As others have stated, the slot drill is designed for plunging in to material and for cutting slots the same width as the cutter.

    An end mill is designed to cut with only one side of the cutter at a time and it should never be used for cutting slots – to get a idea of the problem, imagine a four flute cutter cutting a slot (so it is cutting the full width of the cutter). Picture the plan view of the job, the cutter rotating clockwise and call the direction of the slot being cut the “front” of the slot.

    As one of the cutter teeth cuts away the front of the slot, it will tend to bend the cutter to the left (looking at the plan view) and push the left hand cutter tooth into the side of the slot.  This causes a very rough, lumpy and poor quality side to the slot – this is why you should ever cut a slot with a end mill (or if you do, use a cutter smaller than the width of the slot that you wish to cut and cut each side of the slot separately).  The two flute slot drill does not suffer from this problem as when the front of the slot is being cut and the cutter flexes, there is no other tooth in contact with the slot sides.

    When using end mills the advice to limit the width of the cut to less than 1/4 of the cutter diameter is to minimise the sideways flexing of the cutting tool and the associated problems.


  6. Ah, that makes sense! I knew that an end mill can't be used for plunging unless you've drilled a hole first (or you're using a center cutting end mill). So I guess “slot drill” is just another name for a center cutting end mill. 

    However, I didn't realize that a center cutting end mill can be used to cut a slot to width in one pass. The first time I tried to cut a .250 slot in something I used a .250 end mill and got an ugly oversized slot. Ever since then I've used an undersized end mill and cut the center of the slot first, then cleaned up both sides. It's good to know that with a slot drill I can cut a slot in one pass! Thanks for the heads up on that Ian!

  7. i always use an undersize cutter for a slot, so i can get a good finish

  8. Neat looking project but I'm not seeing how you adjust the diameter of the cut to a certain size or is the idea that you'll have to use a dial indicator to set the diameter of the cut?

  9. Depending how skilled you are, you could put some sort of markings on the job to specify how big the diameter will be. The ones i use at work all have imperial dials on them

  10. Yep, Mad is right. You'd make a dial with markings appropriate for the 1/4-20 screw. Since the screw has 20 threads per inch, one full rotation of the screw equals .050 movement (which would be an increase or decrease in hole size of .100). So you could make a dial with 50 graduations on it and either number them 0-50 or 0-100.

    If you number the dial 0-50 you just need to remember that a change in the radius of 1 equals a change in the diameter of the hole being bored of 2.  

  11. I recently did an associates degree and in my blueprint reading class they never taught me what v. means, all they taught was counterbores, countersinks and such but I dont recognize the V that is in the blueprint for the boring head. sheet 3 of 5 of the blueprints front view center hole right below the 9/32 counterbore. Usually we dont have an X there what does the X mean this is how I know it to be written: 9/32 meaning diameter of counterbore, .61 depth of counterbore. I dont understand what the x is suppose to be there for. As far as the V goes what does V mean? its the v.38x.30. there is more on the left view it shows the v9/32x.50 and under that it shows v13/32x.25 I drew this whole thing up on solidworks the hole in the nut does not line up with the hole in the dovetailed portion that has the hole for the 1/4 20 screw. I went over my prints over and over again trying to find some reason why it doesnt line up perfectly all I can think of is my holes are not accurate, but i cant see how they couldnt be accurate considering they receive a 1/4 20. If this message looks strange its because my wife dictated it for me she is so great to do such a thing for me, however I am an idiot because i dont know what the v thing stands for. Please help!

  12. If the V you're talking about looks a bit like a checkmark, it's a symbol for surface finish (how rough or smooth the part needs to be to function properly). I hope that helps.

  13. How come I can’t download the plans for this? I can’t click the “download” icon