Anyone care to scrutinise some drawings?

For some weeks (yes, really) I have been working on a design for an automatic boring and facing tool. I think that I've now come up with the finished drawings. What I would like is for some kind person to have a look at them and see if they can find any errors which I have missed and point them out to me. I have bought the metal for the project but want to be sure not to ruin it by cutting it up too small - come on, we've all done it! There are six drawings in DXF file format, a brief description in a PDF file and a jpeg of dubious quality reproduced below to give some idea to anyone who's interested.

I should point out that I am NOT a draughtsman, neither am I in any way qualified to present the drawings in any other than a way that I can follow and suits me. That is to say, They are produced for me and by me, as long as I can understand them and make it from them, that's fine. Basically, I'm not after a critique of my draughting ability. Sorry if this sounds a bit haughty, but there are some on here who tend to ride horses of high stature.

Here is the jpeg of the general assembly:

If you would care to help me, please send me a PM in the first instance.

Thank you,

John

Is the gear ratio 12:18? Leads to non integer increments which is not technically wrong just awkward.

You might want to consider the main shafts at right angles to use a worm reduction for finer feed.

It looks like you have two concentric circles of pins, one for in and one for out. It looks like the star wheel shaft moves but as drawn it seems to be engaging both stars at once. I take it what looks like a collar for the spring is actually a gear. I think that needs to be outboard of the star and wide enough to remain in engagement with the layshaft when the star shaft is moved across. Perhaps you have some arrangement not shown to move one set of pins in and the other out and the star shaft is fixed.

Edited By Bazyle on 29/12/2015 13:37:27

I really didn't want to get into a discussion on the merits of the design, but, to address the points above:

The design is unashamedly based on one by Graham Meek, but with some differences to suit my preferred method of construction and available tools. The slide feed screw has an 8mm x 0.75mm thread, so I specifically chose the gear ratio to give a 0.05mm feed per click of the feed screw. As for the pins, they are actually arranged in diametrically opposed pairs so that either one, or both, can engage with the feed wheels, depending on the feed rate required. I admit, the drawing shown doesn't demonstrate that very well, but it makes sense when viewed in conjunction with the explanation and other drawings. Depending on which pin or pair of pins are engaged, the feed screw will rotate in opposing directions to enable boring or facing from the inside-out or the outside-in, so to speak.

John

I have taken up an offer to cast their eye over, so no need to read further, thank you. I look forward to cutting metal soon. Progress and results to be published in a new photo album in due course.

John

You have just said the magic words, "Graham Meek"

If Gray designed the principle of operation, then I suspect it will work perfectly for you.
I collaborated with Gray during his Screw-cutting dog clutch design, and he is a good engineer.

My day job is mechanical design engineer and I can see that your drawing skills are well above the standard of most people who are not in the profession, so don't beat yourself up about presentation etc.

Good luck with the build and lets see it in operation on youtube when you have it finished.

Phil

Graham Meek has sent me the following copy of his original design, which he feels may be usefiul for anyone wishing to compare or distinguish the two.

This also reminded me that a little while back I did a search for 'boring head' articles in MEW over the years, so any 'completists' may wish to check these out:

Neil

I like John's better, the feed system is far more compact and no whacking great knob wailing round to catch the unwary.

Looks interesting, John. Do you have a 3D CAD file or 3D PDF? Easier to understand than a blank and white line drawing.

I love stuff like this - I'm more of a tool maker than a model builder. Hope it works out, so let us know how you progress.

Murray

The whacking great wheel is good for making very fine adjustments when boring but a big dial with a hex socket and a long reach hex key is also good.

0.5mm pitch taps are available in a number of sizes up to 12mm dia at reasonable prices of late. Used for cctv board lenses. They seem to have standardised on the pitch to some extent.

Rather than gripping a knurled rim to face - have holes and put a piece of bar in.

John

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Edited By Ajohnw on 11/01/2016 17:04:31

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John,

I'm not arguing; just wondering ... Do you think that 0.5mm pitch tapped threads would be sufficiently robust in this application?

MichaelG.

Anyone got the method of gearing by which Erikkson with the Tenthset boring head can provide movement in .001mm (.002mm on diameter) increments.

Emgee

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I can only guess that it's a differential screw arrangement, as used on the Norris woodworking planes.

MichaelG.

I feel it should be possible to make up the difference between 40 tpi and 0.5mm pitch by increasing the diameter to over what the usual simple imperial boring heads use.

I have the older model engineer design boring and facing head that could be used on a myford lathe. It uses a pretty simple arrangement for facing and has also been adapted to be used on a milling machine. My over all feeling as I have thought about making one is that it should be possible to arrange for the part that fits on the lathe bed or on a milling machine to be incorporated into the head itself and just holding it in position when facing.

Probably needing to lock it in position when not facing too but things can be spring loaded.

Gears can also allow the sort of thing that Emgee mentions. I get the impression this is usually done by rotating a sort of cap on the top which in turn drives a lead screw some how. I have wondered if there is some sort of planetary gear arrangement inside. Gears do allow any lead screw pitch to be used within reason. Point taken but gears have play, have to be made or bought etc. Also where does it stop. Robust lead screws such as cross slides and screw cutting lead screws use pretty coarse pitches.

John

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Blimey! I didn't expect it to get this much attention. So....

Murray - No, I don't have any 3D drawings. It's about as much as I can do to produce the 2D ones. But if you're offering . . .

Michael - I looked at the thread in my off-the-shelf Asian boring head and that was mighty small, probably in the region of 0.5mm pitch. That's why I've gone for 0.75mm, as I'm anticipating the generated forces to be higher on mine.

As I tried to explain in the post above, the feed screw is 0.75mm pitch - I happened to have one - and the feed wheel has 10 cut-outs, so one turn of the feed screw turns the slide screw 2/3rds of a turn - 0.50mm, thanks to the 12:12:18 gearing. Thus, one feed "click" advances the boring bar by 0.05mm. By having the drive pins arranged in two diametrically opposed pairs, differing PCDs and engaging with the feed wheels at the same differing PCDs, drive can be neutral, selected for an advance of 0.05mm or 0.1mm. There is, therefore, no need for the expense of a left-hand thread. There is provision for holding the feed ring by hand or using a screw-in bar to prevent rotation.

I'm on goodness only knows what version of the drawings - I've lost count - but I think I've found most of the errors and am about to freeze the design. Work has started on the slide and I expect to post some photos in an album in the next couple of days.

Other changes to Graham Meek's admirable design were prompted by the fact that I wanted a bigger one - who doesn't - and what I have available in the way of tooling and materials, etc. For example, I happen to have suitable MOD1 involute gear cutters obtained for a previous project, so I am using them instead of having to make and use a single-point form tool.

I must acknowledge the help I have received from John Stevenson and the encouragement he has given me in addition to a suggestion for further development. That'll be for another day. My brain hurts too much to start on that.

Regards to all,

John

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John,

Apologies for any ambiguity in my question ... I should have addressed it more specifically to Ajohnw.

Thanks for the explanatory note anyway. ... It makes good sense.

MichaelG.

A few people have expressed an interest in this project, so I've started an album entitled "Modifying a Graham Meek design". As work progresses, I'll add some photos and a brief description. I'll not clutter this thread when adding to the album, however. When (if) it's finished, I'll let you know. (If it doesn't work, I'll keep quiet and slink away and cry.)

John

Work is progressing - slowly - but I'm looking ahead to when I can start putting it together. I will need a small compression spring of specific dimensions. Although they are available from the likes of Lee Springs and Flexo, the cost of postage and packing far out weigh the cost of the springs. I was hoping that somebody can point me in the direction of a supplier who will send me one or two springs for the cost of a first class stamp and envelope. I've tried all the usual suspects but to no avail and an ebay search only throws up generic springs or boxes of assorted ones. The size I need is free length = 15 to 20mm, internal diameter = 4.1 to 4.5mm, solid length = 8.0mm, wire size 0.8 to 1.0mm. Flexo No. BM-1937-2M or Lee spring LC035C04S.

Thanks,

John