|Nigel Graham 2||04/08/2022 12:13:59|
|2287 forum posts|
I am slowly (lots of round tuits and other projects, not all in the workshop) overhauling an old Taylor, Taylor & Hobson pantograph engraving machine.
I used a later version, by Rank, Taylor & Hobson, occasionally and professionally, years ago; but can't recall how the cutters were held apart from involving a taper in the spindle and collet-type nut.
Mine lacks that nut.
The thread proved fiendishly hard to identify but eventually I decided it must be 1/2" UNEF (28tpi) - a standard size shown on the Tracy Tools wall-chart I keep by the computer. (Another hangs in the workshop)
So I bought those taps from TT, and made a test-piece from brass.
It did not fit.
Nor did a BSB (26tpi). Nor ME (32tpi.)
Removing the spindle, which is quite simple, made measuring easier and I found it is Unified Special, 30tpi!
Luckily TT had one, a plug-tap.
Ordered Tuesday by phone, it arrived yesterday, and by the late evening I could send an e-post of thank to Tracy Tools, saying I had now made the two nuts I need, for 1/4" and 6mm plain cutter shanks.
I used phosphor-bronze, and had had to screw-cut the bulk with a tiny single-point tool finished to shape(ish) by diamond-file, stone, thread-gauge and magnifying-glass.
Then finish the thread by the tap.
Curiously, parting them off (HSS, rear tool-post, moderate speed) heated them enough to sizzle brushed-on suds and turn the metal a strange dark-grey colour. I have not encountered that previously, making me wonder what this pre-loved bronze really is.
To cut their two spanner-flats (to A/F size consistent with the engraver's other fittings) I made a slightly deeper parting-groove before temporarily transferring work and chuck together to the dividing-head already centred on the mill. This gave a continuous cut for initial and remaining parting-off.
As for the screw-cutting.....
What a saga and cost, trying to make the second-hand Myford gearbox I fitted to the Myford ML7 second-hand from elsewhere, cut even the normal 32 and 40tpi threads, let alone this odd 30tpi!
Its OEM, fixed-centre wheel chain, reversible for screw-cutting or fine-feed, from the recommended 24T tumbler pinion makes it cut threads below 56 tpi only by setting double pitches (select 52tpi to cut 26tpi). To cut 32 and 40 I found needs a 27tooth tumbler wheel I had to buy, and set to fine-feed and quarter-pitch!
I was almost considering reverting the lathe to non-gearbox original trim, calculable for almost any thread you care to name; and am grateful for having kept the original lead-screw un-modified. I did though calculate 30tpi for the little EW lathe sitting patiently in the house.
30tpi? 20T tumbler, screw-cutting chain-mode, select 48tpi.
So what happened then?
Looking for the 20T wheel I found a pristine 12T tumbler pinion in a bag labelled "For extra fine feeds"! In fact a version had come with the gearbox, but for a different tumbler and spindle wheel-set (an older or earlier edition of the ML7 itself - mine is of 1947 vintage?).
So if Cinderella can go to the ball after all... I can now screw-cut the fine pitches easily by gear-box direct selection; but will prefer to use the stronger 24T pinion and half-settings for coarser than 26tpi (Brass).
Oh, more fun..
The half-nuts were very difficult to engage, often mis-engaging and splitting the thread. I had to remove the lead-screw and apron so I could adjust the wobbling, die-cast half-nuts visibly, on the bench, to near-civility; using a piece of ACME studding as test-piece. Their own gib ended up well out of the dovetail....
I still took no chances with the engraver collet nuts; leaving the half-nuts in, slacking the countershaft belt and turning the lathe by hand, using the chuck as the handle. (Being careful not to slacken the spindle thread.)
As for the engraver, that's the most difficult task accomplished but I've yet to identify the spindle's internal taper. I am not sure if cutters are still available (ARC used to sell them) so am prepared to make ones from silver-steel or from broken end-mills and the like.
6694 forum posts
The joy of old machinery!
Yes some bronzes can be tough as blazes to machine and requires a slow cutting speed.
|Adam Mara||04/08/2022 13:05:34|
|172 forum posts|
For cutters try Pantoghraph Services in Leeds, my company has used them for years. They service machines as well, lots on their website.
6384 forum posts
Useful information for an engraver owner. When coming up with gems of info like this please consider making the thread title very relevant and easy for search engines to find so the data is not lost.
There used to be a chap with a website that listed every T&H that came up for sale with photos and other information. Not sure if it is still around but I would expect the owner to have the information you need and needed.
|Nigel Graham 2||05/08/2022 00:54:45|
|2287 forum posts|
Ooh, thank you very much! After a bit of wrestling with the Internet determined nowadys to make finding anything specific as hard as possible, I've located that firm and added it to my growing "Engineering" index.
Apart from cutters it also stocks drive-belts, which frankly are now my bigger problem because I can make cutters suitable for my very occasional needs. Indeed, only last week I ground one from a broken end-mill to engrave rather than scrape the calibration lines on the hand-wheels for a tool-&-cutter grinder; using the milling-machine.
The only fly in the ointment is whether Pantograph Services accepts private buyers. Its site says "suppliers to the trade" - well, naturally, we can't really expect them to expect non-trade customers - but does that mean they exclude any but industrial accounts? (Some companies do.)
Whatever was its composition, the bronze I used machined very nicely, with HSS tooling.
To rough-cut the internal thread I spent a long time with a tool I found I already had, honing it to as near shape as I could; but still to create the lead for finishing with a plug-tap.
The heat discolouring came when parting-off with a tool a bit heftier than it really needed be.
The RTH engraver I used at work was in a bespoke electronics manufacturer. It was used not only to engrave panel labels, but also to cut out the profiled holes for standard 'D'-connectors.
It also came into its own when one day we needed make a special stylus for some sort of plotter. That used two pieces of bronze shim held together by tabs and slits, and the problem was making the slits to shim-gauge, narrow enough to hold the tabs properly.
Testing with some off-cuts, I found I could grind a cutter to a fine enough point to cut the slits, very gingerly. Yes, it did break a couple of times, but I won eventually and the parts fitted as they were intended.
|roy entwistle||05/08/2022 09:15:15|
|1552 forum posts|
I Used to call in Pantograph Services when I was working. Found them very obliging, they would sell brass offcuts quite cheap and always offered advice. I was a private buyer and learned a lot about engraving from them. That was thirty years ago.
Edited By roy entwistle on 05/08/2022 09:16:37
|30 forum posts|
Not sure which spindle you have but I am sure mine is 10 degrees, I made some trial collets ages ago as I couldn’t find them anywhere. Pantograph services had some left but they were not cheap !
They are very helpful, giving me advice to free up the bearings in my bench machine, I think the people there have been with them for years...very knowledgeable.
|Nigel Graham 2||06/08/2022 00:09:24|
|2287 forum posts|
Thankj you Roy, Carl -
I have indexed the PS site.
I would not expect tools like those from a firm like that to be cheap. Their primary customers would be industrial, so the products would be industrial quality; but even simple things like end-mills and twist-drills are not very cheap either.
The collets I made are, strictly speaking, the collet bodies; intended to grip a parallel shank whatever the shape of the tool that enters the spindle. Each is much like a union nut with the coned part shaped simply by the end of the tapping-size twist-drill, with below that a short section reamed; one to 6mm the other 1/4" dia.
I turned a fine groove on the outside of the metric one to indicate that fact, compatible with the identifier groove on the Clarkson 'Autolock' metric collets. (I similarly marked the metric ones of the collets for the 'Worden' T&C grinder I built from a Hemingway Kit.)
For the collet itself, as the torque at the cutting-edge of an engraving-cutter is so tiny, I envisage using an O-ring or a 'Nylon' or brass olive; the radial location being shared between the reamed hole and the spindle. In that case the cutter's fit inside the spindle is less critical, if I have to make the cutters.
Thank you for the angle suggestion. Using your 10º as a start at least, I could test the taper by turning an odd end of rod and trying it with marker-paste. I had considered making a simple taper-gauge: a rod with flat end, concentrically through a larger diameter body, with locking screw. The taper is then derived from the rod end's distance from the ring.
|John Hinkley||06/08/2022 09:25:22|
1356 forum posts
I have just had a quick flick through the lathes.co.uk entry for T&H engravers and in more than one machine spec in the adverts, is states that the spindle takes a parallel shank cutter, but an adapter is either supplied or available as an extra, depending on the model, to take tapered cutters. This implies to me that you can use parallel shank cutters and/or the taper (not specified) is an industry standard across most engravers.
When I had an engraver, a David Dowling type, I contacted Pantograph Services and they were willing to supply me with goods as a private individual. The person that I spoke to even suggested a visit to discuss my needs. (They are fairly "local" to me.) Got to be worth a phone call.
There seems to be a lot of available airspace above the work table, so it might even be possible to mount an ER11, or smaller, collet chuck in the existing spindle to open up even more possilities, such as I did on my Shapeoko cnc router.
Edited By John Hinkley on 06/08/2022 09:33:04
|Nigel Graham 2||06/08/2022 10:51:05|
|2287 forum posts|
Thank you John.
That is very encouraging! I think I do have some information from Lathes.co but will look again.
I viewed an engraver of the same make and probably model as mine, only recently. The owner said he uses taper-shank cutters held just by the taper, which seems a bit chancy!
It was a long time ago I last used an engraving-machine so forget the fine details but am pretty sure the cutter was retained at least partly by some form of collet or nut. The Pantograph Services catalogue shows the cutters having a distinct notch between shank and blade, but I do not know if this is to suit other makes of machine that use a clip and screw system slightly like the ER.
The first problem to solve though is fitting a new drive-belt, already missing when I bought the engraver from G&M Tools (pre-Plague so their warehouse open for customers' viewing and collection). PS may well stock these.
I might treat it to a new motor, too. That fitted is the original, with an enormous capacitor on its outside. It works but I am unsure of its condition. I have at least one candidate motor.
Meanwhile I am also servicing my Harrison L5 lathe, whose cross-slide nut works by remembering where it used to have a thread. Opening up the nut to take the newly-minted threaded bush, I think is for the ML7 as a horizontal-borer, with the between-centres boring-bars in the first outing for their set I made as a Hemingway Kit a few years ago! How to test the hole without needing take the bar off the lathe? A ring-gauge riding on the bar.
Eventual aim: fit the Harrison with a T-slotted cross-slide (either a Harrison original I have but fitted with a different-pitch screw, or an unfinished one that was a recent purchase via the ads on this forum), with an adaptor-plate for the original top-slide. That will lose quite a bit of tool-setting height but the Myford's smaller QTCP will fit the stud, with a suitable bush, so might prove suitable.
6384 forum posts
I think the original TH and D Dowling spindles are taper so that you can replace a blunt cutter with a new one and be at exactly the same height to continue - important for a professional engraver not to waste time resetting the height. Newer ones and larger machines like Alexander die sinkers have collets to take a long cutter. Newing-hall who took over TH used to supply the taper cutters but don't seem to list them any more, Probably no demand as all commercial engravers will use newer CNC machines.
|Nigel Graham 2||06/08/2022 23:54:23|
|2287 forum posts|
TH, and later RTH, assumed not just throwing away blunt cutters, despite professional users having customers to pay for the new one.
They made dedicated grinders for the tools, a bit like a twist-drill grinder, rotating the cutter to created a new edge while maintaining the clearance behind it.
My thought with this one of mine is to sharpen the cutters on the tool-and-cutter grinder, rather as the similar tools, the D-bit cutter or injector cone-reamer.
|Ian Johnson 1||07/08/2022 09:21:47|
|376 forum posts|
Pantograph does indeed sell to individuals not just trade customers, I have used them to supply me with engraving plastic sheet, 'gravoply'. Half sheet or quarter sheet. But you will need to set up an account with them, dead easy to do, and a great company to deal with. Ask them for samples.
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