Boring head, in a smaller size

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
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
My boring head has 3 gib screws. I have them adjusted relatively tight, and I use the center gib screw for locking. So I loosen the center gib screw, adjust the screw, and then tighten the center gib screw to lock it. Doesn't take much time, doesn't mess with the gib adjustment, and holds securely.

Carl
 
I wonder if these modern BH's use differential screw method to achieve those super fine adjustment increments? I cant quite tell what's going on from the cross section. Has anyone come across shop made plans for something like this? Making a dual threaded adjuster shaft like shown in Mr. Pete video doesn't strike me as too difficult.

1690518747658.png



 
Thanks guys for an interesting debate on a subject I have not used often, so have no useful experience to add to yours. I just enjoy learning about stuff, and there is a lot to learn from your experience. On the few occasions II have used a boring head - just a relatively cheap one - I had no issues making the bores I wanted, so didn't think of potential problems and the "best way" to use the tool. But I shall in future.
Most of my "rotating tool" boring (milling machine or lathe) has been with simple bars with cutters locked into their mounting holes. No incremental adjusting screw, just set to a micrometer, and measuring each cut. As I make a "bar for each job" as required, the tools usually are mounted in angled holes, thus the side opposite the cutting point is a useful datum for the anvil of the micrometer..... A simple bit of arithmetic does the rest: micrometer reads = 0.5 × bar diameter + 0.5 tool diameter.
Not so easy with these boring bars where there is no datum from which to check the setting with a micrometer.... So how do you do that? Did I miss something in the discussion?
I haven't watched videos yet, so maybe those explain that aspect.....
There's a lot to digest here, so I must study more....
K2
 
I wonder if these modern BH's use differential screw method to achieve those super fine adjustment increments? I cant quite tell what's going on from the cross section. Has anyone come across shop made plans for something like this? Making a dual threaded adjuster shaft like shown in Mr. Pete video doesn't strike me as too difficult.
Cross section is kind of "not selfexplaining" :cool: .... to me.

Dependent on the function / accuracy it is not really difficult to make a simple differential. The difference between the pitches will give you the advance per revolution. A trap I ran into: The lathe does not do 0.75 mm pitch. (would have been nice) I would go for 1.0 mm and 0.8 mm pitch it still gives me 0.2 mm per full revolution. That would be 0.005 mm if the dial has 40 divisons (radius)

basicIdea.jpg

The basic idea: boring bar holder (yellow) has a boss with a fine pitch external thread. Then the adjuster nut (blue?ish) has internal and external thread, with different pitches. The body (pink) has internal thread to match adjuster. The boring bar will be clamped with two set screws coming from left side. (attention the flat is 90° shifted compared to a Criterion style)
Clamp screw is behind the yellow part pointing towards the viewer.

Problems:
  • yellow part must be kept from rotating and should not wiggle. How to "key" a cylinder from rotating but still smooth moving?
  • Not sure how much backlash this will have.
Greetings Timo

p.s. am I making a boring head that I will never need?
 
.... chopped for easy reading ....

Not so easy with these boring bars where there is no datum from which to check the setting with a micrometer.... So how do you do that? Did I miss something in the discussion?
I did it like lathe work without DRO. I am not too sure if that is the correct way to do it, as I have very limited experience.
  • Make hole somehow. (e.g. big drill or hole saw)
  • Make cut until it cleans all way round; measure diameter.
  • Increase diameter (trusting the dial on the head) cut again, measure bore diameter.
  • sneak up on dimension
  • cut oversized
  • scrap part
  • start over..... :)... or cheat with loctite

 
Hi Timo, been there, didn't waste money on the Tee-shirt, just bought more material and started again but with more Care.
I am looking for a good supplier of "Care", that I can liberally apply to my machining of parts....
K2
 
There are limitations using solid bars with fitted-in cutters.... my smallest being 1/2" bar so realistically about 3/4"bore min. And the largest I have is a 3/4" bar with tool that extends for probably a 1 1/2" max bore..... not needed other sizes. The indexable eccentric tool device could use smaller tools, so copes with a much wider range of bore sizes.... the sky is the limit!
K2
 
Hi Timo, my Dad made a differential screw using 40tpi and 32 tpi dies on the indexing screw. He also made a dedicated micrometer barrel and used a 40tpi thread, with 25 lines on the barrel, scored by indexing the lathe main shaft using a 25 tooth gear against an indexing stop. The main carriage was used to move the scribing tool along the barrel to mark the index lines, at each indexed part rotation of the mainshaft..... and the lathe was made in the 1920s.... When he was made.
K2
 
"Avoid making dumb mistakes" - that's the part I keep having trouble with ... :)

Sorry - - - your response got a laugh out of me - - - - are you trying to have a perfect life?
I find that trying not to "make dumb mistakes" the third or fourth time I do something is hard enough.
Relax - - - take a deep breath and - - - well - - - try again.
(At least here the boss isn't letting you know that you're too !@#$% slow!)
 
I wonder if these modern BH's use differential screw method to achieve those super fine adjustment increments? I cant quite tell what's going on from the cross section. Has anyone come across shop made plans for something like this? Making a dual threaded adjuster shaft like shown in Mr. Pete video doesn't strike me as too difficult.

View attachment 148861



Wow, now THAT is a super precision boring head. I had to watch the video about 4 times to kinda get it figured out. It is built with a somewhat limited diameter range, but the gold colored dial is .001mm/div. YIKES!
It appears to be almost a direct reading setup on the diameter, but I imagine you would need a tomb stone in the tool room to do the actual setup.
The way I see it, the carbide holder/carrier on the top has a single locking screw clearly visible, but it also has a gear drive (not shown in the cross section, but visible in the picture at the very top of the head) to make gross diameter adjustments and then lock the carrier in place. Then the bottom silver dial with a single cross bolt (visible in the pic, but not the cross section) again makes gross adjustments. They call it a balancing screw?? Finally, the top gold dial has a differential lead screw to get the .001mm settings. It also has a cross bolt for locking. It seems like some of the details are purposely omitted from the cross section. At the purple cross section of the gold dial, I wonder if the gray looking discs might be Bellville washers to control backlash. Bellvilles are pretty reliable and can pack a lot of force into a very tiny space if limited travel is acceptable. Petertha, thanks for showing us this. Definitely a super high $$$$ head, but packed with clever ideas. My description might not be exactly right, but I think it is pretty close.
Lloyd
edit- I actually love the Bellville idea for backlash. I will have to use it somehow.
 
I've watched some on Youtube with commercially obtained boring heads using all 3 gib screws to unlock and re-lock the slide. That's simply not necessary. Looking at the majority of the small 2"-3" 50-75mm offshore heads, I'm just about positive the design was directly cloned off the Criterion heads. I know my first off shore head was because I was able to compare them side by side when I finally upgraded mine. And Criterion are quite specific in the user manual about just using that center gib screw as the slide lock. In fact there newer heads are now marked with the word lock just above that center screw. Using all three gib screws upsets what should be a carefully set gib adjustment and allows highly undesirable and variable movement when your trying to make very precise and small movements on the tool slide. So if your currently using all three screws, that could well be a major part of having imprecise adjustments and unpredictable hole size results.

Yes those heads with differential thread systems allow extremely fine adjustments, but it needs to be well understood the manufacturer's would be using sophisticated methods to obtain screw threads with extremely low lead and lag errors in each screws thread pitch. At a minimum, I would guess there being thread ground on specialized equipment that's built to produce those very low error thread pitches. Plus there's a pretty good chance there then being precision lapped to reduce and average out those errors even more. All of that is just part of there very high price that's well outside my budget. If the work is important and precise enough to justify it, I can still measure my boring heads adjustments, admittedly a bit slower, but just about as well using an indirect method. A high accuracy dial indicator to show the amount of slide movement. And no matter how accurate your boring head and tooling is, it's still only half of what's required. Even more expensive is a method of accurately measuring what that hole size being produced really is, any taper, or out of roundness once you start getting below + - .001" / .0254 mm. Luckily and for most of us, that's seldom required other than maybe for bearing fits.

Not to throw Nerd1000,s thread OT, but since those differential threads were brought up. The majority of this PDF would be well above what most of us would ever be doing in a home shop. https://ia800104.us.archive.org/20/...curacy/Foundations_of_Mechanical_Accuracy.pdf But it does detail how much time, effort and investment Moore Tools did trying to obtain those perfect thread pitches for the feed screws and nuts on there jig borers and grinders. They got very close, but could still find and measure those errors no matter how much effort they put into the project. I also happen to think that understanding some of the physical accuracy limitations in what we might be buying or making is still one of the fundamental pieces of information to have for anyone with a home shop. In addition, Moore's clear diagrams about the possible 6 degrees of inaccuracy that may be present in various amounts or even multiple combinations of each one of them was a light bulb moment for my understanding of machine tool alignment and/or misalignment. Its not quite as intuitive or easy as some seem to assume.
 
To confirm Pete's point. Consider a line boring operation (just for discussion) of the boring tool on a lathe mainshaft, and workpiece on the saddle/cross-slide: versus a boring bar between centres acting on the same work piece.
The single supported "boring bar" is a cantilever, relying on the mainshaft bearing clearances, and strength (STIFFNESS) of the cantilever of the tool projecting... versus a boring bar supported as a beam between 2 centres.... the boring bar between 2 centres is MUCH stiffer (typically less than half the deflection) for something the same diameter as the boring tool used in the adjustable boring head. So "configuration of tool" is a major consideration for accuracy of machining.
K2
 
Back
Top