Boring vs Reaming

Currently building a Universal Pillar Tool with castings supplied by Hemingway. The instructions are calling for either boring or reaming of the holes in the arm castings. The two holes are 3/4" and 7/8" both 1 1/2" deep.

Advantages and disadvantages of each technique?
I do have a boring head (but not much experience using it) , but don't have the reamers. Given that a 7/8 reamer is not cheap and not likely to get used again, I am reluctant to invest.

My current plan is to to go down the boring route and practice on some stock before working on the castings.

Any advice would be appreciated

I think you have the right plan. Practice boring on some scrap first. The carbide cutters that come with boring heads often need sharpening before use. For aluminium, HSS cutters might work better.

Or if your lathe is big enough put arms on faceplate and bore with toolpost mounted boring bar.

Given your circumstances, Stuart ... I’m sure you have already made the right decision

Boring is inherently more accurate than a reamer; will be much more economical; and will give you practice with a tool you already own.

That said: I think the best way to bore these parts is probably to use a between centres boring bar.

MichaelG.

[ I hope that gets the discussion rolling ]

Edit: Hopper gets that honour ^^^

Edited By Michael Gilligan on 07/05/2020 10:05:09

Another vote for boring.

-A reamer will just follow the drilled hole so if the drill wanders as it may well do in a casting then th ereamer will just follow.

-Boring allows you to make the hole to fit your shafts which may not be exact nominal size and depending on what spec reamer you buy that may well have a slight oversize.

-Reamers actual cut size will vary depending on material and pilot hole size and you can't easily experiment.

As MG says between ctrs boring bar is more likely to produce parallel bores but often a lot harder to adjust to get that final fit just right.

Do you mean GHT's instructions? If so, I would follow them, if not I recommend you get the book.

Boring is certainly the best way to get the fit needed.

I have the book and it was his instructions that gave the option. Thanks Boring it is.

Actually reamers are more accurate than boring but only if used for final sizing after boring almost to size. But too expensive in this size for a one off job. Boring done carefully wiil do the job.

PS. Just checked GHT's book and he bored the holes in mill with boring head after making plug gauges to get right size to fit Oilite bushes. An addendum by the editor says many since have made it a sliding fit and Loctited bushes.

Edited By Hopper on 07/05/2020 11:15:14

Edited By Hopper on 07/05/2020 11:16:58

I thought the OP was referring to the holes which were not intended to receive Oilite bushes.

I made my UPT to the GHT "words & music". The UPT itself doesn't have any Oilite bushes. The drill head attachment does, 3/8" dia. IIRC. I thought that these bushes need an interference fit to close up to size, so glueing them in place with a sliding fit is incorrect.

I bored my arm castings in the lathe, using a GHT between centres boring-bar. Take care else you spoil a pricey casting!

Incidentally, I don't recall GHT describing any milling machine ops. in his ME articles, it was all lathe ops, but I might be wrong

It is the main arm holes I was referring to. GHT did show boring on the faceplate in the lathe and finshing with a reamer. I will now bore to finished size on the lathe faceplate. . I was considering doing this on the mill with a boring head to get the positional accuracy, but it will be much easier to get the hole fit in the lathe..

Problem is does the inexperienced user order H7, H8 etc reamers to get a specific size and do they even know what size they want and they are more likely to calculate that from a 0.750" starting size when their stock may be a little under, I've already mentioned that the hole produced by whatever reamer will also vary slightly from one material to another and depending on the hole size it is used in. Could be very expensive having to buy a few reamers to experiment which gives the exact size needed.

At least by boring you can work your way up to the size required, typical example I made an oscillating engine over xmas. Nominal 8mm dia crankshaft. Hole in the crank disc was a light press fit and loctited into place, hole in the flywheel was a firm sliding fit and bearing a smooth running fit but as I bored all holes I could get the size I needed rather than 3 different reamers that may have performed differently on the three different materials

Different in a production enviroment where someone would have got the right fit first and then just push the reamer through time and time again.

Stuart

Before setting up for boring the castings may I suggest you make some GO/NOGO gauges, you can make a stepped end with small diameter changes, this will aid getting to the required diameter bore without tears.

Emgee

It is worth noting the GHT faceplate setup, bore the 3/4 ends first and then set the reference boss on the faceplate to give the correct centre distance for the 7/8 holes, do not move the reference boss until both arms and the arm for the drill if you are making it. This should ensure the centres of the arms match perfectly without having to measure. It is more use that they are all the same rather than the measurement being precise. My column is 0.8805” so I will have to bore to fit. It is a nice piece of ground hard chrome plated bar so worth the trouble I think.

Mike

So you want a hole at x spot that runs true to y axis etc , etc so you drill a hole , now you need to bore it to make it run true before you ream it so why don't you just bore it to size anyway ?

That way you have full control and you cut out an operation that uses a tool you may not own !

Thanks all, some great advice there

Another point in favour of boring is that you make all the size measurements with your equipment. So it matters not at all the the nominal 0.875" rod measures 0.872" or 0.878" with your equipment. You simply verify the error between your internal and external measuring kit and make the sizes required to get a nice fit. If the internal kit says 0.874" and the external says 0.876" when the sizes are just so you just have to take a bit more care in writing the target measurements down and setting the lathe cuts.

The readings my be wrong way round but its the actual size that matters how you get there isn't terribly important.

Working with errors like that would (now) drive my temper needle two laps past "danger UXB (nuke)" in the red zone but in over 40 years I've managed to accumulate the good stuff. Folk starting out are unlikely to be as fortunate. Back in young, hairy and optimistically enthusiastic days I've coped with similar.

Of course that sort of error completely wrecks any chance of good results from a reamer bought to suit a measured size. Which is why the professional shops pay serious money to keep things calibrated. It should perhaps be noted that measuring equipment of any decent brand holds scale accuracy remarkably well over many years of use. Most errors on anything not obviously worn out will be end point setting.

I'm not a great fan of go-no go gauges for this sort of work. I prefer to shoot for a measured size one or two cuts short of the target and set the slide dial to zero for that point. Having made the cut, and spring cuts if boring, on zero I then check the diameter and reset the zero for the final diameter. With typical home shop machinery its best if the same depth of cut is used on the first approach to zero and on subsequent ones. Not forgetting spring cuts before measurement. Working in that fashion can be a little tedious but nice fits equivalent to tenths thou level accuracy can be produced on any lathe whose condition is noticeably better than "right old nail".

Hafta say that I tend to use 50 thou (imperial) or 1 mm (metric) cuts for pretty much everything beyond the "rush a lot off quick" stage unless the job is too small. Keeps the maths simple. Maybe I'll halve it for a finishing cut should the material demand such. Easy with the machinery I have and appropriate for what I mostly do.

Its worth finding the sweet spot for your equipment. Invariably this will be less than the machine is capable of if worked to its full performance but the time taken for extra cut or three is rarely of import on small jobs when stacked against a lower risk of error or possibly overloading a tool requiring time out to re-sharpen.

Setting the slide dial so either the final cut or the last but one "measurement" cut occurs on zero can be a good habit. Yep, I've done the finish on 0.687", drat, shoulda been 0.678" thing a time or three or (be honest) more.

Clive

Could I just point out that the critical parameter for the pillar tool is that the bores in the arms are the same distance apart. Whatever system you do employ the set up should be such that the machining of the second bore is carried out by directly referencing it to the first bore. In my opinion all the holes should be bored either on the lathe faceplate or on the mill. The bores can either be brought to size by boring if reamers do not wish to be purchased or by reamers after boring to reaming size. I would say that the second process is best, boring to establish consistant centres between the bores and reamg to bring to identical size. That way the user can be assured that the arms will allow the bores to be correctly aligned and bushes that may be interchanged bore for bore.

regards Martin

Stuart, as some have said already, for accuracy step 1 is to drill, step 2 is bore to just under finished size, and then ream. This is how I made thousands of gear blanks years ago with a tolerance in the bore of 1/4 of a thou.

If you are a beginner I would suggest it is easier to get an accurate hole first time with a reamer. As a beginner It is easy to make a small error if you bore only. It is also easy for experienced modelers to make errors when relying on boring. If you already have some round bar for the job, and you bore your casting oversize then you will have to correct things somehow.

If you join a local ME group maybe you could borrow one from a fellow member. It is not so easy at the moment, but keep your eyes peeled for job lots of used reamers, and build up a collection.

Chris Gunn

3/4 reamers are on ebay for 10 quid. I'd buy one for that.

I've found you vary from GHT's instructions at your own risk.

At least with reaming your holes are all dead same size and you make your pillar and collars all to suit that one size. But if you can bore to plus or minus half a thou you might be ok.

FWIW,

If making a fit between a shaft and a bore, I would produce the bore first, and then turn the shaft, if possible to suit the bore.

Turning tools are less flexible than a boring bar, so it should be easier to produce the sort of fit that you want, without taking continual spring cuts. And as a last op, if you want, the finish can be polished with emery and oil.

Howard