Diy adjustable boring bar for small holes

[Savedbygrace77]

Hi there, I have a southbend 9 and a mini mill at home. I decided after 4 years to tear down my (italian!!) 80 gallon DevilBliss air compressor only to find the rod size is superbly whack - and totally messed up .. not worth dumping more $ into it i decided I will mig alu weld the piston and rod and re-machine them and hold thumbs Yes I know I can get a whole head unit but this is for fun and hopefully it will last.

Either way, my mill has a drill chuck and R8 too, I was thinking of making a VERY simple HSS bit holder with a square groove to hold the bit and a set screw to maintain position- I would have to make a measurable side cut to get an est cut size with calipers.

Has anyone made something simple?

Here you can see how bad the rod is worn down (bushing is gone), piston has a light score that I will also be repairing and honing to a nice fit - I will be sourcing a cheap bushing somewhere and doing a final fit -

 

[Savedbygrace77]

back to the actual machining, im going to try clamp the small piston in my 4 jaw and see if i can get a good index off the existing rod bushing hole as opposed to mucking about on the mill with a round object-

 

[rons]

Get some religion.

 

[Doozer]

I have bored connecting rod journals in the lathe on a faceplate. This was before I had a good boring head for my mill (back in the day). I think I was modifying a rod for a Tecumseh engine for whatever reason. But doing the job on the lathe may be your best bet, unless you have an offset boring head. But I would sell some spunk and buy a new rod and piston before going through all that.

-Doozer

 

[Terry Keeley]

I'd just get a new rod, that one is pooched.

 

[rons]

Copy one of these to whatever size you want. All of them have a swivel tip. They fit into a long extension bar.
They are for wood. I would figure out what angles I want for the tip and design the thing from tip to other end.
If you have a small broken carbide drill bit...



These are from Robert Sorby tool company.

 

[gbent]

Set up a dial indicator with a large flat tip to aid in adjusting the boring bar. Remember you are measuring movement on the radius.

 

[Savedbygrace77]

nice rons will take a look thanks.. I just realized I have a cheapo fly cutter set I can turn down/modidy the tiny one on the lathe and see if that works... sth like this. Will modify the cutter with a round nose for a smooth finish..

 

[neanderthal mach]

I used a fly cutter and crudely re-sharpened brazed carbide tool to bore a through hole with a dial indicator to set size increments before I bought an actual boring head once. And that was on a much smaller and even less rigid mill than yours. Yeah it worked sort of ok, but an awkward, long drawn out pita. And calipers are about worthless for measuring any accurate inside holes to less than about + - .003". Use that SB to machine your own go-no go gauge that you can measure with a mike for your finished size.

There's more than enough YT videos around that weren't available back then you should be able either build your own version of a small boring head or just spend $100 for an off shore head. There utter crap and the usual included boring bars are 10X worse. I finally junked all that and bought Criterion heads and bars, there obviously not the worlds best, but light years better and much easier to get accurate bores. Even used but still decent Criterion heads can be found for roughly the same price as one of those import heads. I get that even at a hobby level this isn't cheap. It took longer than I'd like to admit to finally figure out the better tooling is in fact well worth whatever it cost. And Micky Mousing something barely above wood butchery levels is rarely cost effective in time, money, frustration, or almost always with the finished result. Even with the exact same methods and equipment today, I could easily do a much better job. The difference now is I wouldn't want to unless there was no other choice.

But I sure as hell didn't hold that fly cutter shank in a drill chuck, use an actual collet. And if you don't have any yet, then buy those first. Drill chucks are for axial loads. Today I now have what I think is a half decent Taiwanese BP clone, power spindle feeds, multi axis dro, inside mikes etc, as well as those boring heads. I also don't miss anything about those early days and never enough of the correct tooling. In hind sight, a boring head should have been bought long before I did simply because of how much it can increase your accuracy and capabilities.

 

[kenton]

That welded aluminum is going to be about as soft a chewed bubble gum. You will need very sharp tooling to get a decent cut.

 

[Woodhandle]

Machining oil groove in motorcycle con rods, had a batch of 30 to do.

Boring bars for use in the vertical mill. This one is set to the diameter of the receiver ring of a M700, I use for milling scope mounts.

When in doubt use a boring head. I have both larger and smaller.

 

[Savedbygrace77]

I saw those cutting heads but did not realize one could insert a smaller too into it- (noob me) - darn ill prob order one right away.. thanks woodhandle..

Also will use the R8 collet system, i was going to final hone it the last thou- its an air compressor not a hotrold so worst case ya know, itll go boom or clank or work for a few years.

 

[rons]

When in doubt use a boring head. I have both larger and smaller.

I'm getting or making a bar for a carbide insert. The HSS bars I have made in India are mediocre. Haven't used that word in a while.

 

[Savedbygrace77]

mounting a piston on the table will be a new thing for me, luckily its small so I might manage with v-blocks somehow but honestly if it fits in the lathe even better!

 

[eKretz]

It's going to be a flip of the coin whether it goes boom right away, not knowing the alloy used. I'd be looking to buy a rod for sure. Or make the whole new rod, if you just have a bug to machine something.

 

[michiganbuck]

Is that the pin end or the crank end? Pin end running dry?
Is it a standard size a reamer could finish?
Might you use an oillite bushing.
Use a boring head if doing on a mill because holding .001 or .002 is really difficult any othe way..A home made BB that you can micromerter over might be OK..
face plaet on a lathe is easy.
(X) dont even think about attempting to boreing a hole in aluminum with a surface grinder..

 

[wesg]

'mediocre'

I find 'crappy' easier to spell correctly.

I had a relatively large c'bore to cut. I used a flycutter with a hand ground tool on the mill. Make a cut, measure, and offset the table by half the correction. Loosen the screws and slide the tool to lightly touch the bore.

I was surprised how accurately this could be adjusted. Just have to remember to move the table back to zero before each pass.

Saved the back breaking work of pulling the chuck off the big lathe to use the faceplate. And, unlike some people I've worked with ... put the damn chuck back on when I was finished.