Boring head, in a smaller size

[Nerd1000]

I've wanted a boring head for quite a while, but the regular ones are far too big for my mill. Here's my solution to that issue.

The body is 37mm in diameter, and it takes 10mm tools. I made the attached tool from silver steel. The m6 lead screw with 50 divisions on the dial makes for 0.02mm per division.

 

[timo_gross]

Congratulations to the finished tool, you can make more tools now with the small boring head.

Is your picture upside down, or is that a horizontal mill? For a horizontal mill and small diameter boring between centers might also be an option, provided you are not making a blind hole.
Saw a nice youtube video about a kit that Andrew Whale made on his youtube channel.

I used a single point cutter to make some holes. I think a proper jig to advance the small HSS cutter is the key to keep it usable.

Another type I did not see yet as DIY project is a version with a horizontal bore instead of the dove tail. A plug is inserted into this bore. The boring bar sits again in a cross drilled hole in the plug. The screws to clamp the boring bar are on the opposite side of the dial. Maybe you can tell from the pictures what I mean.


The disadvantage is that the adjustment range is limited. Fine adjustment works good. And the balance is not affected as much because the moving part is less heavy.

Greetings Timo

 

[Nerd1000]

Yes it's a horizontal mill. I have pondered a line boring setup, but haven't come up with a good solution for adjusting the tool position.

 

[SmithDoor]

I've wanted a boring head for quite a while, but the regular ones are far too big for my mill. Here's my solution to that issue.
View attachment 148579
View attachment 148580View attachment 148581
The body is 37mm in diameter, and it takes 10mm tools. I made the attached tool from silver steel. The m6 lead screw with 50 divisions on the dial makes for 0.02mm per division.

I have one about that size and does not fit I go to standard boring bar. There are two ways to adjust the tool bit
Tap to adjust this takes to learn .
The next is make a micrometer adjustment that fit the boring. This takes time to make. After making this tool the adjustments arf easy.

Dave

 

[pete]

George Thomas in his book The Model Engineer's Workshop Manual has an excellent design for horizontal boring bars with a 40 tpi screw for the tool adjustment. To me, that was worth the books price alone.

 

[Lloyd-ss]

Sweet! Nice Job! Necessity is the mother of invention.
I agree that standard boring heads are often require a modification to your set-up to deal with the extra length.

You used an M6 bolt for the lead screw? Did you make the dial?
Using a boring head is so much fun when it goes well.
Lloyd

 

[Nerd1000]

Yes I made the dial. Conveniently I already had a 50 tooth wheel for the atlas mill's indexing head, so I made a simple D bit engraver and engraved a brass disc, which is attached to the leadscrew via a m3 hole in its end. I used a threading tool mounted on its side to 'shape' the matching groove in the body.

I'm pleased to report that the head is quite precise. I used it to machine the lifter bores in my diesel crankcase and had little difficulty hitting the sizes i wanted, then discovered to my dismay that I got the positioning wrong (it's sometimes hard to see what you are doing on a horizontal mill, and i haven't yet learned to double check apparently) and scrapped the whole part, literally on the last operation. Ugh.

The only issue I've had is with a bit of flex in the long boring bar needed to reach those holes, the bores were tapered and needed multiple spring passes to straighten them out. I think this is because I'm only using a single set screw to hold the bar in the boring head.

 

[Lloyd-ss]

...............................

The only issue I've had is with a bit of flex in the long boring bar needed to reach those holes, the bores were tapered and needed multiple spring passes to straighten them out. I think this is because I'm only using a single set screw to hold the bar in the boring head.

(quote snipped for brevity)

Again, nice job. I will ask, but I think I already know the answer. You don't have any broken solid carbide tools that you can grind into long boring bars to help with the flex?

 

[Nerd1000]

(quote snipped for brevity)

Again, nice job. I will ask, but I think I already know the answer. You don't have any broken solid carbide tools that you can grind into long boring bars to help with the flex?

Sadly no. Though it's a good idea.

 

[pete]

The only issue I've had is with a bit of flex in the long boring bar needed to reach those holes, the bores were tapered and needed multiple spring passes to straighten them out. I think this is because I'm only using a single set screw to hold the bar in the boring head.

That may not necissarially be the problem. Fwiw, my Criterion heads only use a single set screw to fix the boring bars in position as well. There also fairly large in comparison to the bar diameter, so increasing your set screw size might help a bit. The same brand of boring bars I bought with it fit the boring head holes really well. There's good evidence the bar holes in my heads are ground given the fit and surface finish, so I suspect they were high precision jig ground to final size after hardening with maybe .0005" clearance between the also precision ground boring bar shanks and the fit of the holes in the heads. Criterion also add a single ground flat to the bar shanks in the correct position for that set screw. My heads do have a horizontal through hole for doing outside the heads normal boring size capability, with that and the correct handed boring bar, it can use 1,2 or all 3 set screws to secure that boring bar, but that's more the design used on these heads than a must use all three requirement. That fit between the holes in the head and bar diameter is the most important, those set screws only need to secure the boring bars against any radial or axial movement within the hole itself. With a shop built boring head, I think I'd ream or if possible single point bore, then ream the holes to a known size to fit my chosen bar diameter.

Since the Young's modulus is the same for any hardened or unhardened mild steel, boring bars in reality have zero difference between the material there made from and the amount of extension you would have when turning on a lathe without tail stock support as an example. In ball park numbers, roughly 3 times or really pushing things and with very sharp tooling, maybe up to 5 times the bar diameter for bars built from mild steel, and solid carbide might move those numbers up to around 7-9 times there bar length outside the head verses the bar diameter. Yes you can and sometimes we have to cheat a bit, but those would be the rough numbers for overall bar rigidity between the two materials. I also bought a set of what Criterion call stub length boring bars, there made purposely short with a variety of cutting tip diameters and specifically made to work around that unavoidable bar flex problem. Using a boring bar that's too long isn't really needed for much of what we might be doing, although there are obvious exceptions. But any extra length as you've found can sometimes work directly against what your trying to accomplish with those tapered holes.

 

[awake]

Well done! I made a boring head in a similar size; in my case I was aiming for imperial units, so used a 1/4-20 screw and a 50-division dial to give adjustments of .001" - can go a little finer by aiming between the divisions - and 3/8" diameter boring bars. I've gotten good use out of the unit, but I would like to make a larger one to take 1/2" boring bars to bore larger / deeper holes with a stiffer tool.

 

[petertha]

@Nerd1000 nice tool. Did you utilize some existing plans or design it yourself?

I've always had a fantasy itch to make something with a reduction rear using fine module pitch to achieve finer bore resolution. I have a feeling some heads might do this in some manner, but those cost about the same as my lathe. My boring head is 0.001" increment between lines so hitting target dimensions for things like bearing pockets can be hit & miss. I tried to think of a way to micrometer across the head using embedded reference balls or something. I'd experiment on my own creation but don't really want to drill holes into my commercial tool.

 

[awake]

Petertha, the YouTube creator named MrPete222 (aka Tubalcain) made a couple of recent videos describing a method for fine adjustment using differential and opposing screw threads. The second of the videos shows a small boring head for which a full revolution of the dial produces only .010" of movement in the slide - thus, with 50 divisions on the dial, each division represents only .0002" of movement.

Here are the videos:

 

[Lloyd-ss]

Andy, I had seen a similar type of double thread used in a precision leveling device for shipboard navigation equipment but had no idea what the technique was called. Elegant in its simplicity, and now it has a name!

I have a question for all boring head users. (I don't mean people who are dull in the bathroom...ouch) Depending on the size hole you are boring, and the direction the tool is pointed, the lead screw in the boring head can either push the cutting edge outward, or pull it outward. I can see pros and cons for both techniques. And do you loosen and tighten the gib screws for each adjustment. Does anyone have a strong case for one direction over the other?
Thx, Lloyd

 

[timo_gross]

Andy, I had seen a similar type of double thread used in a precision leveling device for shipboard navigation equipment but had no idea what the technique was called. Elegant in its simplicity, and now it has a name!

I have a question for all boring head users. (I don't mean people who are dull in the bathroom...ouch) Depending on the size hole you are boring, and the direction the tool is pointed, the lead screw in the boring head can either push the cutting edge outward, or pull it outward. I can see pros and cons for both techniques. And do you loosen and tighten the gib screws for each adjustment. Does anyone have a strong case for one direction over the other?
Thx, Lloyd

It may be dependend on the internal construction? I have two boring heads (both I do not use very often). The cheap hobby grade (sub 70$) was not so much fun to adjust, because there is backlash in the adjuster and sometimes it "brakes loose", then I have to back it up a lot and start over. It is easier to adjust it turning clockwise.
Commercial ("rel. cheap model") one is much more easy to use the dial. The boring bars have only one flat, so the direction (clockwise) is given by tool position.

The Wohlhaupter brand ones have a fairly complicated mechanic. It allows to change diameter during operation. Inside the bore. e.g. for internal ring grooves.



I also saw some version with an electric motor and wireless adjustment , probably a very involved diy project.

 

[petertha]

Petertha, the YouTube creator named MrPete222 (aka Tubalcain) made a couple of recent videos describing a method for fine adjustment using differential and opposing screw threads.

Absolutely brilliant. Thanks for those links!

 

[Nerd1000]

@Nerd1000 nice tool. Did you utilize some existing plans or design it yourself?

I've always had a fantasy itch to make something with a reduction rear using fine module pitch to achieve finer bore resolution. I have a feeling some heads might do this in some manner, but those cost about the same as my lathe. My boring head is 0.001" increment between lines so hitting target dimensions for things like bearing pockets can be hit & miss. I tried to think of a way to micrometer across the head using embedded reference balls or something. I'd experiment on my own creation but don't really want to drill holes into my commercial tool.

View attachment 148829

It's my own design but heavily inspired by other builds I've seen.

 

[awake]

Andy, I had seen a similar type of double thread used in a precision leveling device for shipboard navigation equipment but had no idea what the technique was called. Elegant in its simplicity, and now it has a name!

I have a question for all boring head users. (I don't mean people who are dull in the bathroom...ouch) Depending on the size hole you are boring, and the direction the tool is pointed, the lead screw in the boring head can either push the cutting edge outward, or pull it outward. I can see pros and cons for both techniques. And do you loosen and tighten the gib screws for each adjustment. Does anyone have a strong case for one direction over the other?
Thx, Lloyd

The direction of travel may be dictated by the design of the boring head - or at least, for the one I made, there is very little room for adjustment when screwing inward; accordingly, essentially all adjustments are made screwing outwards. I don't think there is an advantage one way or another; either way one must account for backlash, but as long as one keeps adjusting in the same direction, that should not be a problem.

I used to loosen and tighten the gib screws each time, but that quickly got very old. I experimented with leaving the gibs very snug but still adjustable, and find that it works just fine. Particularly with the 3/8" size of the boring bar, and even more if there is very much length to the bar, one is limited in the size of cut, and within those limits I have not seen any tendency for the cut to change the setting. One issue is, if the gibs are too tight, it may be hard to adjust in small steps, so it is a balance ...

 

[Lloyd-ss]

The direction of travel may be dictated by the design of the boring head - or at least, for the one I made, there is very little room for adjustment when screwing inward; accordingly, essentially all adjustments are made screwing outwards. I don't think there is an advantage one way or another; either way one must account for backlash, but as long as one keeps adjusting in the same direction, that should not be a problem.

I used to loosen and tighten the gib screws each time, but that quickly got very old. I experimented with leaving the gibs very snug but still adjustable, and find that it works just fine. Particularly with the 3/8" size of the boring bar, and even more if there is very much length to the bar, one is limited in the size of cut, and within those limits I have not seen any tendency for the cut to change the setting. One issue is, if the gibs are too tight, it may be hard to adjust in small steps, so it is a balance ...

Andy, ok, you and I agree on the adjustment method and direction, for better or for worse. And I also noted what Timo said about the adjustment "breaking loose" and more or less having to start over. That has happened to me too. I probably just need to take my boring head apart and lap the sliding surfaces, stay with light cuts and just keeping the gib screws snugged up, and not overly tight.

And also avoid making dumb mistakes and snapping the bar off. More than once. Darn. I think that's why they sell the little bars in sets.
Lloyd

 

[awake]

"Avoid making dumb mistakes" - that's the part I keep having trouble with ...