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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: Pratt Burnerd 4 Jaw Chuck
24/10/2021 10:38:23

They are a tight fit in their holes. No other method of retention.

It is prudent to keep pins, jaw screws and slots together so they go back in the same way they came out. If really fussy, mark rotational orientation as it would be possible to reinstall 180 degrees out.

Examine them well and stone off any burrs resulting from the removal process before reassembly.

Beware on reassembly that if the forks are twisted (rotated) it can make operation of the screw very tight.

Reassembly can be made a little easier if the chuck is warm and the pins are cold.

Thread: Collets for Myford tailstock
23/10/2021 10:56:42

Particularly with regard to the Morse taper collets (with limited grip range), have you confirmed the shanks of the taps you want to use fit a standard collet diameter?

The ER collets might work better as they have a range of gripping diameters.

Thread: A workholding question.
22/10/2021 07:52:22

Tin the brass parts and the steel stub with soft solder. Sweat them together. Cut all at once.

Alternatively, superglue instead of solder.

You did not say how (which direction) it moved. Are you cutting to compress the double-sided tape or to expand it? If it moved downwards or sideways, a flat stop in the appropriate direction will prevent this.

To me, the steel stub looks a little on the small side. Something the same diameter as the brass would give more surface area for the glue. Clearly, you will cut into it the first time you use it.

Thread: Trugrip conversion
20/10/2021 17:28:25

The major diameter is 1.238". If you want to verify, buy a 5C collet and measure it.

I am guessing that the thread form is 60 degree included angle.

Most of the major threading insert manufacturers provide tables showing the infeed for a particular pitch and thread form.

Below is one example. Another very good one is the Seco one:

https://www.mitsubishicarbide.com/application/files/5314/7191/5783/tec_threading_depth_external_en-us.pdf

Use the numbers as a guide. The final dimension you require depends a lot on the cutting tool you use - a hand ground HSS one will be different to a multi-pitch insert (A, AG, G, etc.) and will be different to a single (specific) pitch insert.

If you are set on this route, it might be wise to buy your collet set and cut a test piece in the same material as the real version to verify that it fits every collet. If you cut the final version to a set of numbers, what happens after the chuck is assembled and one of the collets does not fit?

Thread: Spacing of buttons for making involute cutters
20/10/2021 09:00:33

Resurrection of a 7-year old thread...

I have just stumbled across the following, which provides a method of calculating button diameter and spacing that I had not seen before (the computing power just was not available to Ivan Law when he wrote his book). The paper itself is only 31 years old.

https://www.geartechnology.com/articles/0990/Approximating_an_Involute_Tooth_Profile/

Direct link to the paper itself:

https://www.geartechnology.com/issues/0990x/bilhardt.pdf

If anyone wants to duplicate his computer program, there is a very elegant solution for fitting a circle to three points here:

https://stackoverflow.com/questions/28910718/give-3-points-and-a-plot-circle

Thread: Hi all, newbie with first lathe, rare one i think.
19/10/2021 14:26:54
Posted by wayne ollerenshaw on 19/10/2021 14:09:40:

I will redo the check again tonight. Will of been me and a newbie to the world of lathes making a mistake like that.

As Herr Michael Gilligan suggests above, a photo of the Gewindesschneide Tabelle will mean you do not need to measure anything - the info. on the plate will tell you. Think of it like the label in your trousers - you do not need a tape measure to size them, you just look inside and see FB.

19/10/2021 12:23:12
Posted by Dave Halford on 19/10/2021 11:26:41:

Which would be quite handy for a metric German naval vessel crew.

Makes you wonder about the story.

Yes. It is interesting to note that the two shown on the German site linked to above are also imperial - they are both gearbox models and the screwcutting charts are shown in the two discussion threads.

In one of the German site discussions, the poster says the bearings were marked GDR, so East German. However, that may have no relevance to dating this one.

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.

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