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

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.

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 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

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.

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

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

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.

Bore it!

Turn up a go-no gauge as in the book and you'll be fine.

Made mine probably twenty+ years ago an it's one of the most used tools in the workshop, mainly for tapping.

The original GHT handle was not at all user friendly so I made up my own.

Forget the sensitive drilling attachment as more modern alternatives available now.

For tiny taps the original Eclipse chuck works well.

For bigger taps, an ER11 collet chuck which can pass through the arm with the nut removed.

For even bigger taps a Jacobs chuck with a bayonet to disconnect the handle so it will pass through the arm.

Boring versus Reaming? They're not deadly enemies, surely both are valuable.

My take on reamers is they are the fastest way of finishing a hole to an accurate size. Step one, drill or bore an ordinary hole, close but not particularly accurate or straight. Step 2, apply reamer to finish hole accurately.

Boring can also produce accurate holes but it takes longer and needs more skill, especially measuring the bore and not overshooting. Peter mentions 'no-go' gauges, a good way of speeding up. A big advantage of boring is the hole can be of any size whatever – it's not limited to standard reamer sizes. And big reamers cost big money!

My old book on high-precision work using buttons and other tool-room techniques to make jigs, fixtures and gauges doesn't mention reamers at all. Straight holes with precise diameters positioned at exact X,Y locations are bored, not reamed. I guess a tool-maker would still use reamers and other ordinary methods for any part of the job not needing high-accuracy?. However, this book shows ultra-accuracy was done by boring very carefully and checking with calibrated measuring tools.

It's an interesting book, but I've never had occasion to use any of it's methods – they take more time, concentration and skill than I have, I don't need that level of accuracy, and I don't have any way of measuring the results. My tool-box can't realistically guarantee better than ±0.02mm. Unless I use a reamer!

Dave