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Member postings for DC31k

Here is a list of all the postings DC31k has made in our forums. Click on a thread name to jump to the thread.

Thread: KLG Mystery Object.
18/10/2021 17:47:50
Posted by Ian Johnson 1 on 18/10/2021 17:35:46:

Looks like a bottle opener? One of those freebie corporate giveaways?

You are correct. See near the bottom of this page.

https://aipetcher.wordpress.com/2011/11/02/a-life-in-a-year-2nd-november-motorways-and-minis/

Thread: Ball screws
13/10/2021 17:12:59

If you are converting a machine, then asking about ball screw diameter is rather putting the cart before the horse.

Decide on the machine and make some drawings of the space available for the nut and screw. That will then guide you in the diameter. Ball nuts for a given screw diameter are somewhat bigger in all directions than standard nuts.

Thread: Halogen Oven
12/10/2021 19:51:34

Every one I have fixed has been left hand thread.

Are you absolutely sure it is the element?

Maybe 4 out of 5 that I have fixed, it has been the thermal fuse that has gone.

Check it with a continuity meter and if it is open circuit, temporarily bypass it and see if the element comes on.

Thread: cutting spur gears on a mill
11/10/2021 07:04:01
Posted by Andrew Johnston on 10/10/2021 20:47:33:

If a hob produces a mathematically correct involute curve rather than a series of facets why do some gears need to be shaved after hobbing to improve profile and reduce running noise?

What you are asking is precisely analogous to asking why turned parts need to be ground or lapped after they come off the lathe - the answer being to improve the surface profile.

A great number of the gear finishing tools use the same motion as the gear cutting tools that preceded them, just with a different cutting tool - often an abrasive.

Pete Rimmer's point is very apt. Nobody complains about a lathe producing a helical surface. One can extend his point to the flat surface produced by a shaper or planer - at a microscopic level it is a series of ridges, but the tool/workpiece relative movement is correct.

There is a huge amount of confusion in this place over what constitutes an 'approximate' method. A lot of it is simple misunderstanding of the language used.

A generating process is by definition one in which the movement between cutting tool and workpiece is geometrically (mathematically) correct to produce the shape required. It is a mistake in the use of language to employ 'approximate' to describe a 'generating' action.

Where 'approximate' might gain some foothold is in the _application_ of the method. If you do not let the hob cut 'enough', the sides of the gear teeth will not be well formed (cf roughing cut and finishing cut with a lathe - coarse and fine helix left on the work). The definition of 'enough' is arrived at by the end-use to which the gear is put. Sometimes, even 'forever' is not 'enough' and that is when you have to send the gear to another machine for finishing, just as you would send your planed surface plate to be scraped.

10/10/2021 11:06:29
Posted by Nigel Graham 2 on 10/10/2021 00:01:52:

Going back a bit nearer topic I am fairly sure the Myford manuals tell you the gear standards...

It is a strange thing. Of every manual for every machine tool that I have ever come across, the gear specification is never mentioned.

As a few examples: Myford 7-series; Colchester Bantam, Chipmaster, Student; Harrison L5, 140, M-xxx class; Boxford. Look at every Asian-sourced lathe available new from UK suppliers - how many of them mention the change gear spec.?

You might also explore mills that use change gears (e.g. Harrison, Deckel, Alexander, early Beaver).

It is notable that change gear specs. are hard to find on lathes,co.uk, perhaps the most comprehensive resource available.

Also surprising is that in the many years since the web has been part of our life, no-one has produced a compendium of this information.

Thread: Routing
07/10/2021 19:07:26
Posted by Derek Lane on 07/10/2021 18:31:39:

The parts are routed before assembly and then mitred to 45 deg. otherwise you would end up with rounded internal corners.

No mitre is needed with the cutters he is after.

The generic search term is 'stile and rail cutter'. As suggested, Trend's or CMT's catalogues will give you a good overview of what is available.

Thread: What lathe does this steady rest fit?
06/10/2021 08:41:14

The paint has not aged well since it last appeared here:

https://www.model-engineer.co.uk/forums/postings.asp?th=34868

Thread: gr 8.8 ht bolt steel which carbide tip
05/10/2021 21:26:01

Thanks for the scan.

Looking around, it appears that a Grade 8.8 bolt is roughly equivalent to EN19 or 4140 steel. The steel has a similar ballpark UTS but its yield strength is lower. Were EN19 a bolt, it would be graded approximately as 8.6 rather than 8.8.

05/10/2021 19:47:59

I wonder if it is worth noting that 'Grade 8.8 steel' as such does not exist.

Fasteners are graded as 8.8, etc. but you cannot buy steel stock in this manner.

Maybe someone who knows the grades could give us an approximate comparison of bolt grades and steel grades.

Thanks.

Thread: Chain Protection Sleeve
05/10/2021 17:31:02
Posted by Clive Foster on 05/10/2021 16:12:39:

Its amazing what you can find these days from folk like RS et al.

Those popped up just searching for 'cable sleeving' as my mind went blank on the proper term. I have now remembered that a generic search term is 'braided sleeving', e.g.

https://www.hypex.co.uk/Techflex-Sleeving-and-Heatshrink/Heavy-Duty-Sleeving/Gorilla-Sleeve/

https://www.hellermanntyton.co.uk/products/expandable-braided-sleeves (polyamide and even aramid are available)

Another source for the siliconised fibreglass stuff is catering equipment suppliers, and as Nicholas' post above shows, it is also widely used in performance vehicles. My only concerns with this stuff are that it might trap moisture as it not very breathable and it might be somewhat baggy on the chain.

Thread: Small metric setscrews
05/10/2021 16:00:58

Only in brass or tin-plated brass here:

https://prime-miniatures.co.uk/catalog/bolts-hex-head

https://www.ba-bolts.co.uk/methex.html

Thread: Chain Protection Sleeve
05/10/2021 15:51:12

Please see if any of the following RS part numbers provide some inspiration:

668-1254

668-1273

668-1239

Something tough enough that works on the Chinese finger trap principle might do.

Thread: Small Hydraulic Press Tools
03/10/2021 15:34:57
Posted by Michael Gilligan on 03/10/2021 15:13:01:

...Do you think that my little Hilka 2-ton bottle jack is actually likely to see such pressures

It would be possible to do some fag packet calculations. If you know the diameter of the jack ram, you know its area. With the 2-ton on that area, you have a pressure. The same pressure will be on the pump ram and the mechanical advantage of the operating lever can tell you how much force you need to push on it. Vertical movement of main ram will give you a volume that the pump ram has to move. Vertical movement of the pump ram will tell you how much volume per stroke and thus how many strokes from closed to open. Pick a speed at which you want it to operate (e.g. closed to open in 30 seconds) and you get a flow rate.

Thread: Indexing Plate
29/09/2021 15:18:40
Posted by Emgee on 29/09/2021 14:14:47:

Measure the PCD of the 36 hole circle and the chordal distance between hole centres, the dimensions obtained will allow you to calculate the exact hole position for the additional hole

On a 200mm PCD (i.e.100mm radius), the difference between the midpoint of the chord and the correct position on the PCD is a little under 0.4mm.

A smaller PCD will have a proportionately smaller error (i.e. 50mm radius is under 0.2mm error).

Is it worth worrying about considering how the hole might be marked out and formed and the likely tolerance and fit of the indexing pin?

The value of the error can be calculated from e= 0.0038 * PCD/2. (i.e. 0.2% of the PCD).

The 0.038 is 1-cos(5 degrees), 5 degrees being the half angle between holes.

Thread: Turning (approximating) a Domed Surface
27/09/2021 18:51:26

It might be worth drawing or visualising what he wants to do before making too many more suggestions.

Using the 50mm radius and 25mm diameter mentioned in the first post, the curve pokes out about 1.6mm at its centre.

Thread: Startrite Mercury MkI nutset threads
23/09/2021 20:58:52
Posted by Jon Halland on 23/09/2021 20:16:05:

I grew up metric and have lived happily so far...

And if it turns out to be a BA thread, you can continue to do so.

BA _is_ a metric thread.

Please see: http://www.stubmandrel.co.uk/workshop/18-reference-information/23-are-ba-screws-metric-or-imperial

23/09/2021 18:50:42

British, and associated with electrical fittings, have you eliminated the possibility of 4BA?

Chronos sell a BA thread pitch gauge should you need one.

Thread: cutting spur gears on a mill
20/09/2021 15:19:53
Posted by Dave S on 20/09/2021 14:39:54:

I suspect with appropriate CNC magic and a pointed V cutter you could actually cut a number of mod sizes and any tooth count with just one cutter

A tapered cutter is not necessary. Assume your A-axis is aligned with your X-axis. If you move in Y- and rotate in A-, that presents the side of a parallel cutter to the stock in the correct manner.

What sets the upper limit of the cutter diameter is the root detail of the tooth (i.e. part geometry). What sets the lower limit is the more practical issue of length-to-diameter ratio.

Please have a look at Gearotic, written by Art, the originator of Mach 3. There is a 'gearheads' forum associated with the software where historical posts can be seen. You will see a number of contributions there by John Stevenson who was closely involved in the development of the software.

Thread: Screw cutting
20/09/2021 12:13:24
Posted by colin hamilton on 20/09/2021 11:42:59:
I'm not sure what a native metric lathe is.

OK. Your Continental Chipmaster is a native metric lathe. Its leadscrew and all its feedscrews are metric, as are the dial graduations. A native imperial one would have the corresponding items in imperial units.

It is possible to cut metric threads on a (native) imperial lathe and imperial threads on a (native) metric lathe using a translation gear. When you do this, it is generally necessary to leave the half nuts engaged for every pitch you cut.

When you are cutting a thread in the same units/language as the leadscrew, there are instances where you can disengage the half nuts even without a leadscrew indicator and other instances where you need the indicator to tell you where to re-engage them.

It is worth looking at the ISO metric thread diagram here: https://en.wikipedia.org/wiki/ISO_metric_screw_thread

It does not have sharp crests or a sharp root. If your home-made tool has a sharp point, the infeed distance after touching off on the stock will be different to if it has a flat end. The total infeed distance for a metric thread is never 'H' in the diagram above as 12.5% of that H lies outside your stock. The minor diameter you have calculated is possibly for an internal thread and the diagram shows the relationship (or difference) between the minor diameters of external and internal threads.

For an imperial lathe, one, single thread dial indicator will work for all pitches you would normally cut. For a metric lathe, this is not true. At this stage, let us just say that metric thread dial indicators are more complicated than imperial ones and that is why many manufacturers did not chose to fit them.

It would be wise to read the Chipmaster manual very well and understand what bits are inside your Continental version. Martin Cleeve's book is a goldmine of information of screwcutting, including tool grinds.

20/09/2021 11:21:05

Pick a pitch (and diameter) like M16 x 1.5mm such that you can disengage your halfnut.

You would do well to mention in this conversation that it is a native metric lathe rather than us finding this out by chance from reading your other recent contribution.

Give some numbers: what minor diameter are you using; what stock diameter are you using; what cutting tool are you using; what is your total infeed in both straight ahead and in angled mode?

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