# A 54 mm boring head for my mini-mill



## Anko (Mar 30, 2011)

Hi to all

I got started with a boring head proyect, I got almost finished now, because I dont had the time to post it before..

The idea is to made a 54 mm boring head for my mill that accepts my 1/2" carbide boring bar set, with a MT3 shank, all in a 70 mm heigth.

First the MT3 shank, the material is 1020 steel, in the desing I was looking for a threaded and taper union, because I believe that just a thread union will not give me a concentric fit all the times I get the boring head apart, but that concept (taper and thread)requires much heigth for the union (the goal is that the max heigth of the tool was 70 mm) so I got a shot for a taper union (1.5°) and a screw that work like a drawbar to secure the taper shank, the pictures will tell better I think:












For the body I got to decide what kind of dovetail fixture I will use, In my research I have found 3 ways to make it:






I choose the n°3, because at the present time I haven´t had good experiences with regular gibs, but this desicion will need a close fit in the dovetails, all the body parts where turned to 55 mm.

All the body pieces are 1020 Steel:





















and... 8)






total failure jajaja ;D no matter all my efforts the dovetail fit was not close enough (very close for my first time) and the set screws needs incredible force to flex the metal, and the area of touch was a tiny line with the screws tight at maximum strength

To solve this problem I go to plan B, cut the failed gib and made the n°2 type of gib, the square end one:






this gib worked great, next step is machine the rest of the bottom piece (the one that holds the boring bar)











And make a little preview:






Now come the time for the lead screw and nut (M8x0.5), the material is Silver steel, this will require the make of a custom tap, I cut the lead screw and the tap in the same bar to get a matched set screw and tap:






with the advice of the forum members (thanks to all) I hardered and temper the tap and set screw, then cut the nut out of brass, afther that I made the assembly of all the pieces to put it in the lathe for cut it down to 54 mm of diameter (finishing cut)











Here a terrible mistake was taken, the lead screw should be a left hand type, not the rigth hand, but is already done now.... 

In the same setup I drill and reamer the holes that accepts the boring bars, the result was:






All Through all the considerations I couldn't get the nice finish I was loking for, I turned the boring head with 1000 RPM and a recent sharped hss finishing tool bit (with a large radius tip) and make a very thin pass, but it not worked good as I expected, but later sand paper do the job....

And the present status of the project is all finished exept for the dial face, I will made out of brass, the boring head is in working condition, but I havent made a cut yet..

Here is what it looks like: 8)






has been a very fun and learning project! im thinking on put a counter weigth bar to reduce vibration, and ofcourse some thing to prevent rust (I tried oil but it rust anyway, grease is better working but Im trying to find aother solutions) any ideas are wellcome! ;D

Saludos!


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## picclock (Mar 31, 2011)

Hi Anko

Thanks for the pictures, it looks like a good project. Probably something I should have a go at as I don't have a mill boring head (probably cos I bore stuff on my lathe).

I'm sort of puzzled about the gib arrangement. If one side is at right angles what's to hold the slide 'up' on that side ? Do the adjustment screws penetrate the gib to prevent vertical movement ?

Very impressed by your tapmaking skills - it looks like it came out very well.

For the rust I have found out (by accident) that if I use lard as a cutting lubricant on steel this seems to prevent rust forming. I don't know if its just the lard itself or a combination of the heat when machining with the lard but it does seem to work. My vertex rotary table always seems to want to rust, despite WD40 and various other oils/greases, however, steel parts made using lard lube and stored next to it show no signs of rusting (yet - its been about 3 months). It may just be that the steel types are different but it might be worth an experiment. For application I just warm the lard a little and apply with a brush.

Best Regards

picclock


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## Anko (Apr 4, 2011)

Hi Picclock

sorry but I dont undestrand you very well, lard... do you mean the...cooking stuff??? ??? (my english is more or less not good)

about my tap making skills this is my frist tap I ever made, I have to ask for advice in the hardening subjet to archieve the tap making, I dont know if was the small pitch and larger diameter that made the tap cut great in brass!

About the gib, the set screws should fit in the position holes, but they not should penetrate too much.

Anyway thanks for the response!

Saludos


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## Holt (Apr 4, 2011)

Hi Anko
Very nice looking boring head, sorry about your dovetail failure, would have been nice if it had turned up as you had intended. For the adjusting screw, its only a matter of getting use to it, and it will work just fine Thm:


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