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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: Gear Cutting - Pressure angle.
01/04/2020 19:58:27
Posted by AdrianR on 01/04/2020 18:00:03:

From what I can see on helicron this method creates an approximation to the involute curve by cutting a number of facets on each tooth.

The method is one well-recognised in industry and is by no means an approximation. It is a method of _generating_ gear teeth, the same as hobbing or gear shaping. Have a look for Sunderland gear planer. There are a few posts on this forum by John Stevenson that have discussed the method. There are numerous books available on the internet archive that discuss generation methods.

01/04/2020 17:54:45

My goto online reference for all things gearing, at KHK Gears says z=2/sin^2(a) where is tooth count and a is pressure angle is what determines minimum teeth for no undercut when using a rack-type cutter.

https://khkgears.net/new/gear_knowledge/the-first-step-of-mechanism-design-using-gears/know-about-parameters-that-determine-gear-shapes.html (Section 3)

Thread: Connectors for multiple LED lamps
28/03/2020 18:31:12

Search Google for 'xlr multicore stage box' or 'xlr punched panel'. Maybe your best option is to buy an empty box and the correct number of sockets and assemble it yourself.

Thread: Metric thread cutting on a Colchester
25/03/2020 19:20:34

Colchester is a brand of lathe, just as Ford is a brand of car. Ford made Mark 1 Cortinas, Escorts and Capris.

You need to find out exactly what machine you have and obtain a manual for it. Read that manual very well.

From the tooth numbers of the gears you give, it is possible that you have a Colchester Student. If so, kindly read this thread:

https://www.model-engineer.co.uk/forums/postings.asp?th=150056

Thread: DIY induction motor rewind
24/03/2020 07:05:08

This is speculation, so view it critically: if you know the resistance of one of the good coils and the diameter of the wire, you can calculate the length of the winding and hence the weight. Wire manufacturers usually publish resistance per kilometre for their products. If not, you might have to go back to first principles and use resistivity of copper and cross-sectional area.

23/03/2020 18:51:21

Brocott UK. Have everything you need, including the proper varnish which is probably better.

Lots of Youtube videos on rewinding, mainly in Urdu but with enough English to understand.

Pay very good attention to the arrangement and winding direction of the coils.

Just about to try to rewind my coolant pump motor.

If the motor is not working, you will have to strip the windings so just weigh the old ones.

Thread: Lathe Advice - Colchester
23/03/2020 16:12:40

I wonder if you are limiting your options by deciding so soon on one of two particular models. With second-hand machines of this type, condition and accessories are probably more important than manufacturer and model.

If, for example, a fully-equipped CVA came along at the right price, would you turn it down? Monarch 10EE? Small DSG? Harrison M-series? And do not discount the Eastern European lathes; they were superbly built (and natively-metric).

I would be deciding on a centre height and bed length and going from there.

As for specifics of the two you mention, as Stuart said, the Student is L-taper and chucks and backplates are expensive. The D1-3 of the Chipmaster is also less popular (and hence more costly) than D1-4, which is common to Far East machines.

Out of the box, the Chipmaster has a better speed range (30-3000rpm, providing you retain the variator) than the Student, good for small stuff and modern cutting tools. Its spindle bore is a bit small and it is a bit short between centres. Requires two extra and non-standard change gears to cut 1.75mm or 3.5mm pitches. Built for people about 4' 6" tall. Check it has the 4 1/2 to 3 Morse spindle bush with it. The bed stop is good to have to take advantage of the autofeed trip (but someone has them available for circa. £50 on eBay). Chipmaster/Bantam steadies seem to command unreasonably high prices if missing.

You need to find a long-term Student owner to tell you all the niggles with that machine.

Have a look at the language of threads you want to cut and make sure any machine you buy will do what you want and has the gears with it if necessary as these can be difficult and expensive to track down.

Edited By DC31k on 23/03/2020 16:14:29

Thread: Record no 1 vice jaws seized - removal?
23/03/2020 07:29:15
Posted by Kiwi Bloke on 23/03/2020 03:17:00:

It used to be possible (may still be for all I know) to buy special vice jaw screwdrivers. These were stubby things, of hexagonal section, to take a wrench and/or cross-drilled for a tommy bar. The 'other' end was pointed, intended to sit in the slot of the opposite jaw's screw. The driver was engaged with the screw ro be removed, and located in the opposite screw by gently tightening the vice. Cam-out prevented! You might be able to use one of the screwdriver bits intended for magnetic drivers, etc., but a larger diameter is better for the gorilla-like forces usually required.

It is good to hear that the right tool exists. I have lost count of the number of Youtube restorations I have seen where they first dismantle the vice and then try to remove the jaws. Use the vice itself to assist in removing its jaws.

A cut off and ground down allen key would do the job. As well as the standard 1/4" A/F hex bits, they also come in 8mm and 10mm A/F.

A lot of vice jaw screws have a non-standard countersink angle and sometimes are quite a low head. So it is worth preserving at least one of them as a pattern for making replacements.

Thread: Measuring size for vee belts
22/03/2020 08:28:29

From the information kindly given by Nick above, you could draw the belt sections full size on a cereal box, cut them out and offer up to the pulleys to see which fits best.

Thread: What are you reading?
21/03/2020 08:41:41
Posted by Joseph Noci 1 on 20/03/2020 21:32:57:

Are there any folk here using a Kindle?

I have had one since 2013 and have not bought a book yet. There are innumerable older books on there that are totally free, which might assuage your concerns over licensing.

E.g. Mark Twain; all of Dumas' (both of them) works; Shackleton; Conan Doyle; Dickens; Austin; G.K. Chesterton; Hugo.

Something I did not yet see mentioned in this thread is the enormous amount of free material online. The Internet Archive is a good place to start.

A few notables I have found: Foundations of Mechanical Accuracy, Joshua Rose Modern Machine Shop Practice, Skunkworks (Lockheed), Truth, Lies and O-rings (Space Shuttle), Ashley book of Knots.

Thread: Packed Boring Bars
18/03/2020 06:15:26
Posted by Brian Wood on 24/10/2019 10:52:40:

...it was rather frustrating not to get a view of the holding arrangement on the saddle end of the boring bar.

It is well worth perusing other videos by the same man. He does some very interesting work.

His lathes are repurposed very large turret lathes, so the cutting tool is held in the turret, hence the need for cut adjustment at the sharp end.

Thread: Source of CZ106/108 brass bar UK
17/03/2020 07:42:26

Sorry to post again. This forum software does not allow editing...

https://www.metalsupplies.com/products/brass-flat/

says 'some sections available in CZ108'

17/03/2020 07:37:32
Posted by Robin Graham on 16/03/2020 23:41:54:

l've emailed Thames Stockholders asking if they can supply in small quantities

If you need a couple of metres, then one standard stick of bar (3m) should be OK . I would be inclined to call them and see what is their most popular line in this material and to whom or the type of customer to whom they sell it. Then if the order is too small for them, you have some leads. You may end up up having to buy something of bigger cross section and cut it down.

This may be a stupid idea, but what about buying sheet, melting it down and casting it into bar?

16/03/2020 07:49:26

Thames Stockholders say they have it

https://www.thamesstock.com/cz108-brass-alloy.htm

Thread: Cutting Parameters for Small Slotdrill
15/03/2020 19:17:02

If there is raised lettering, as already said, a tapered cutter will give a more true to cast appearance.

Will you use air blast to send the chips away?

I wonder if a ball end mill would help in this situation.

APT seem to have a good price at the moment for cutters of this size.

Thread: What am i doing wrong
10/03/2020 20:29:26
Posted by old mart on 10/03/2020 19:38:06:

I f you don't have the luxury of a taper turning attachment, you have to advance the compound by hand. This makes an even speed very nearly impossible.

You can jury-rig a power compound slide using a cordless drill on the handwheel nut. That may improve the finish.

Thread: change wheels
09/03/2020 06:33:53
Posted by noel shelley on 08/03/2020 22:06:53:

A) What pitch ? 1.25Mod ? B) What do they belong to? They look old.

The numbers you give match up with 1.25MOD.

Oldness does not necessarily mean they are imperial spec. Europe, with its metric system, has existed for a long time...

Are you familiar with the method of identifying gears? Measure OD in millimetres and divide by (number of teeth +2) for metric. For imperial, divide (number of teeth +2) by OD in inches. This will help you work out the ones you think are Drummond.

Thread: Imperial Electronic Edge Finder
07/03/2020 15:46:44

Look on Zoro for:

4200-520 Linear Electronic Edge Finder

Zoro also have imperial shank manual ones, but not details on tip diameter (and overall length is given in metric!).

For example:

https://www.zoro.co.uk/shop/hand-tools/centre-finders/double-edge-finder-0-500inch-body/p/ZT1002024X

[Edited to say that Zoro's offering is the same as Linear (Chronos) but twice the price!]

Edited By DC31k on 07/03/2020 15:49:32

Thread: Holding block for ISO 30 shank
04/03/2020 20:23:17

If it is only for indexing, can you use the hexagon ER block and grip the narrow parallel part of the 30 taper where the drawbar goes? The challenge then is secure clamping when milling.

Thread: Colchester Student mk1 change gears
03/03/2020 20:44:54

Looks like there were a couple of different versions produced. The Student is quite a long-lived machine so changed through the generations.

Drew's plate is the same as the bottom four lines of Ian's plate, so is missing some of the finer threads.

It is interesting that Colchester did not provide for standard M12 1.75mm pitch threads on either machine. The same omission is made on the Chipmaster.

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