Tool or its arrangement which would do opposite reaming

[abdulbadii]

What is the tool or its configuration/design which would do opposite reaming: lessening a rod diameter slightly quite precisely?

Tactile need is rod diameter ~ 5 - 20 mm get lessened by 0.1-0.3 mm

[themadhippy]

A Lathe

[abdulbadii]

mean a portable one

[T3sl4co1l]

There is such a thing as an "external reamer" but I think most hits are for pipe deburring tools, i.e. the blade geometry is conical to make a chamfer.  Not a cylindrical cut.

There does still seem to be something like that, but I'm guessing it's rarely used.



I'm also guessing one like this isn't very useful outside of a lathe anyway, certainly not if you want any consistency.  It looks like it's a single-point cutter too, but I can imagine one being made with multiple flutes like a regular (ID) reamer.

Tim

[EPAIII]

There is no such tool in common use. But almost anything can be made. I once made a special tool to chamfer the ends of 1/4" aluminum rods. It mounted in a hand held, electric drill.

Tell us more about what you are doing. What level of precision you need? Material? Size? One time a year or thousands of pieces a day? You know, those pesky details.

mean a portable one

[dmills]

Lathe or a cylindrical grinder?

Granted 0.1mm off a diameter is perhaps more then a cylindrical grinder is really appropriate for, you can do it but it is going to chew your grinding wheels up.

[TERRA Operative]

Emery paper in one hand and the workpiece in a battery drill in the other hand?

[Overspeed]

Hello

You can use a boring head with a bespoke tools holder to machine OD . that often used to machine trunnion on milling machine

Depend of the diameter you need and the lenght to machine , you can also used a magnetic annular drill cutter

Regards
OS

[coppercone2]

You can use a OD lapping tool for this, it will just take a while, IMO 0.3mm is achievable, maybe slow. Its not that much material.

I was kind of surprised how fast ID laps cut into soft metals. I mean rotary mechanized lapping with diamonds on a drill. I never tried a OD lap, but ID laps are certainly useful, i.e. you can use it to deburr a deep cross bore hole that has a burr in the middle of a deep bore (on the inner surface of the bore that you bored into)... but its kind of hard to control you know? If you have a three screw lap you will have to lap a little, measure, adjust, lap, measure adjust until you get it right. Just keep in mind if you do a deburr with a lapping tool, you will have a expanded region in the middle of the bore, where the lap spins the most while its removing the burr and also deforming the interior, but if you don't spin the lap in the entrance of the bore too much, the diameter there should remain close to nominal.. its not proper use but it works.


I would consider this a PITA on steel, on aluminum/copper it might be OK

Now If you have something sticking out of something you can't spin and you need to lap it, you would need to spin the lap, which is going to require some kind of adapter, usually you would spin the shaft and then lap. It takes a while and doing it by hand would probobly require a 'flight of the phoenix' or 'African Queen' scenario, like getting trapped in the desert having to convert a car to a motorcycle (what a tale), fixing a boat in a war zone or building a plane in the desert.

Keep in mind there are various grits of lapping compound, you want something aggressive. And you would want to make a relief cut around the perimiter of the shaft you are lapping to make a area where the lap can move freely (i.e. you are not running the lap into the side wall that is being formed), so you would first need to run across the shaft with grinder to make a score around the whole thing, then lap the area after the score, and when you are lapping part of the lap will move over the area that is relief cut. I.e. if you want to remove 0.1mm of material 1cm deep on the end of a shaft to fit something, you would need to cut say 0.15 - 0.2mm deep score line x 2mm (or more) wide 1cm from the end of the shaft, I think, because if you don't , the lap will climb on the uncut area while you are doing the lapping motion, that 2mm is a guess, you would need to determine what traverse oscillation distance the lap require, and make the score line of that width, and deeper then the final cut,.If you don't do this, I expect you will get a conical taper rather then a cylinder.

https://www.carbideanddiamondtooling.com/External-Laps-and-Lap-Holders-.0625-to-4.25-Inch-Diameter-ID-20361-

[JacobPilsen]

There is such a thing as an "external reamer"

mapal.com/en-us/a/external-reamers -voellm

[T3sl4co1l]

Identical to the "OD reamer" I found. Guess some do call it that after all!

Tim

[Psi]

Emery paper in one hand and the workpiece in a battery drill in the other hand?

i was just going to say that.

It can be pretty precise if the paper is fine and you keep checking with calipers.
Can also wrap an entire sheet around the rod and hold tension on it to take metal off evenly.


I guess ideally you would just buy a portable lathe

[Overspeed]

Hello

Lapping tool don t allow to generate square shoulders and that not designed to remove a lot of material , lapping is in the 0.001 inch of depth cutting

IF you have an access to a lathe and a shop drill that easy to built a clone of a mapal tools ( mapal is a very high quality tool but the price is $$$ ) from a steel round piece and use a hand grinded HSS cutting bit rather a carbide insert . For quick and dirty that also possible to built one by using steel bar and arc welding / MIG welding steel plate , as that a single point cutting the driven shank with generate the geometry .

HSS square or round bar will allow to set the final OD after machining and also allow to re-grind it if the cutting edge wear , with two tools set for different diameters ( rougher  and finishing ) 

Regards
OS

[coppercone2]

I think you are underestimating the material removal rate from lapping with bigger grits. I have tried one of them ID tools on a drill and it certainly removed soft metal pretty fast. Slow as balls compared to drilling, but it was easy to expand the bore too much. 0.001 inch goes quick.

Have you tried machine lapping? Also, you need to frequently put more abrasives when you are hogging the lapping tool.


Like its touch based. You feel the resistance start to go down as it expands but also as the diamonds wear out. I use alcohol spray bottle and a box of wipes with the tool to expedite things. Diamonds are very friable compared to other abrasives i believe.

I do wonder what kind of improvements you would have by using a CBN paste rather then a diamond paste for lapping also, they are way tougher.

BTW I am assuming the person wants to do a 1 off with basic tools to fit a bearing or something.

[Overspeed]

Hello

I make lapping and honing of precision surface since 25 years , I agree that IF you have time ...a lot of time .. you can remove some raw material ... with a lot of tooling wear as your surface wear a lot  . and with abrasive pastes progression in grain size . BUT you will not get a sharp square angle between the original diameter and the honed surface

If that you use a far easier process by using abrasion '' quick and dirty '' a electrical drill + un hand grinder and that do the job as the poor '' tool post grinder '' solution

The tool I have described in my previous post as inverted boring head , I have no time to make a video of my tooling .



Regards
OS

[coppercone2]

Ok, I figured this guy wanted a hand tool. That thing is not portable. I can't think of another way to make it semi accurate portable. I can see some kind of attempt being made with a small drill press.. your process is great but will it work without the stiffness of a milling machine?


I have my doubts the lapping thing would even be satisfactory, but if you are desperate to try something...

and you need to admit you want to know what would happen if someone tried to put a OD lap on a power drill to reduce the size of a shaft end held in a vice......

[Overspeed]

Hello

a hand tool ? to machine an outside surface round ( circular + cylindrical ) ?? that start to be complicated as the problem is to control feeding and centering in the same time .

In old mechanical school that a shop exercise to make a round bar from a square bar with a file and finish it by using abrassive paper but that request skills and training and more if you want to keep your round surface centred to another .

With a file that a multi flat making and control the dim with a caliper for each flat done , recut the edge to make smaller flats up to have some thing like a hectogon ( 100 flat ) and after finish by sanding to remove the edges

with a hand grinder and two wises



Regards
OS