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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: Buying a Propane Torch
28/10/2019 19:25:31
Posted by Andy Carlson on 28/10/2019 17:54:56:

I don't want to start paying for those medium sized gas cylinders that hang off the bottom of the next size up handheld torch so my thinking is to skip a step and go for something with a hose that can run off the same propane cylinder that I use for the BBQ.

I do not know if this will be germane to your issue, but it is something I only recently discovered: Rothenberger, I think, make an adaptor that screws into the torch that the medium-sized cylinders hang off and allows it to run off a standard propane cylinder via a hose. If you have one of these torches already, it gives you the best of both worlds: cheap propane gas on a tethered torch and 'cordless' MAPP on the disposable cylinders.

Thread: Boxford metric lead screw fitted to imperial lathe?
28/10/2019 19:15:36
Posted by Brian Wood on 27/10/2019 18:37:09:

You have the right idea, but what DC31k has omitted to say is that the driver on the spindle (after the reversing gears) will be 20T and the gearbox entry spindle needs a 56T gear in all cases.The change gears are fitted in the chain linking those two.

Sadly, and I hate to have to point it out, but there is one error in his table in the listing for 1.75 mm pitch. The change gear ratio should read 7/8, which could be 35/40 as you have interpreted the ratio.

Thank you for the clarification and correction.

I am glad that it has been peer-reviewed and the bugs worked out so speedily.

I think I was a bit wooly in my terminology when I used CG for change gear ratio: it should have been more closely defined as change gear ratio modification to standard ratio (thus, when it is 1/1, there is no modification to standard/factory needed).

The incorrect 4/7 came about as I started off with 7/4 and 24tpi (i.e. gear up 1mm pitch to get 1.75mm*). That needed an extra 20t wheel added to the set (35/20). To reduce required number of change wheels, I realised you can gear down 2mm pitch but did not do well in changing the numbers. It is fortuitous that the correct 7/8 or 35/40 can come from the existing set.

Brian's calculations on getting you imperial pitches are to be highly commended.

Maybe it is bad form to recommend a different author, but Martin Cleeve's Screwcutting book is essential reading. He spends a good bit of time talking about non-standard leadscrews (mainly for speed in production work).

* And if anyone has an imperial Chipmaster, that is how you can get the missing 1.75mm on this machine, with a 63/36.

27/10/2019 11:22:52
Posted by JasonB on 27/10/2019 10:09:26:

Well I can get the 100/127 to work as 100/127 x 3.175 = 2.4999997 so near enough 2.5

but when it try 135/127 x 3 I get 3.1889763 not 3.175

Unless I'm doing it wrong.

We should keep firmly in our heads that we are discussing machines with a (Norton) gearbox. The ratios in the gearbox of a native imperial machine will be different to those in a native metric machine. The imperial Boxford above is a good example - it has, for example, a ratio with an 11 in it. You would not find a native metric machine with an 11 in its gearbox.

[Interestingly, it has a 23, half of which is 11 1/2, used for American pipe threads but not UK ones and does not have a 19 which we do use. Uncle Tony's site says it was a copy of the US South Bend and this is very apparent here].

The difference in gearbox ratios affects our choice of translation gear, so a gear to go from imperial to metric on an imperial machine will differ from that used going from metric to imperial on a metric machine.

If I might say so, there is no place whatsoever for decimals in any discussion of screwcutting. To avoid confusion, fractions are the only acceptable currency. One inch is defined as exactly 25.4mm, or 254/10 or 127/5.

Thus our 8tpi leadscrew has a pitch of 1/8" or 127/(5x8) = 127/40 mm. If we drive this with a 100/127 combination, the 127's cancel and we get 100/40 or exactly 2 1/2mm .

This is where use of decimals and a calculator lets us down. With fractions, you can see the numbers and you know that the 127's must cancel, so you know that one side of the multiplication sign has to have 127 as numerator and the other side of the multiply sign has to have 127 as denominator. If you have a 127 gear, the conversion will always be exact. If you come to a place where it seems approximate, you have taken a wrong turn somewhere.

Now onto our 3mm pitch leadscrew and our 135/127 gear. 1mm is 5/127 inches. 3mm is 15/127 inches. 15/127 x 127/135 gives 1/9 inches exactly. So our 3mm pitch leadscrew is behaving as if it is 9tpi. This number seems strange at first sight, but it probably combines better with the metric-native ratios in the gearbox to give the required imperial pitches.

27/10/2019 10:38:03

OK, assuming it has the same gearbox as that shown at http://www.lathes.co.uk/boxford/page7.html BUT with a 3mm pitch leadscrew, the following should work.

mm is metric pitch required. TPI is gearbox setting. CG is change gear ratio. Only needs 35, 40, 45, 50, 60 and 70 gears with one duplicate. Best to copy and paste somewhere using a monospace font.

mm TPI CG
3.0 8 1/1
2.5 8 5/6
2.0 12 1/1
1.75 12 4/7
1.5 16 1/1
1.25 24 5/4
1.0 24 1/1
0.9 24 9/10
0.8 24 4/5
0.75 32 1/1
0.7 24 7/10
0.6 40 1/1
0.5 48 1/1
0.45 48 9/10
0.4 48 4/5
0.35 48 7/10
0.3 80 1/1
0.25 96 1/1
0.2 96 4/5

27/10/2019 08:02:33
Posted by JasonB on 27/10/2019 06:25:08:

You can get the imperial threads buy using the same 135/127 approximation...

I am confused by the above. Is it simply a typo? Surely if you have a 127 gear and use it correctly, it is no longer an approximation but is an exact conversion.

To the OP, your fundamental issue is working out all possible input: output ratios of the gearbox, forgetting at this stage the change gear train (or set or assume it is 1:1).

You need to see what one turn of the gearbox input shaft does to the output shaft. If you do this systematically for all possible lever positions, that will tell you the ones that will be useful for metric screwcutting.

If you look at the picture here: http://www.lathes.co.uk/boxford/page7.html the left lever is a range lever, that goes from 0.5:1 (A) to 8:1 (E). My guess is that B is 1:1, hence the numbers in the B-row are likely to be the actual gears in the gearbox (the tooth counts seem sensible for a Norton gearbox).

Thus use of the 16 setting will be useful in gearing your 3mm leadscrew by factors of 2 (1.5mm, 0.75mm). The 18 setting has a factor of 9 in it which might not be useful (Jason's original post above where he says try 18tpi for 1.5mm is, I think, a typo - it should say 16tpi); the 20 a factor of 5 (0.8mm or 4/5, 1.25mm or 5/4); the 22 a factor of 11 (not too useful for metric, unless you want 5.5mm or 11mm pitches); 23 not useful at all; 24 has 3 in it; 26 has 13 (not useful); 28 has 7 (perhaps for 1.75mm 7/4).

Your overall calculation will go: [change gear ratio between spindle and gearbox input] x [range box ratio] x [Norton gearbox ratio].

Edited By DC31k on 27/10/2019 08:03:15

Thread: Pratt Burnerd 4 jaw Chuck jaw alignment
22/10/2019 07:26:38
Posted by Hopper on 21/10/2019 23:20:53:

Number of jaws makes no difference. You still need to preload them to hold them in the working position and to stop them moving about during grinding.

Perhaps I stressed the wrong word in my previous reply. For a four jaw INDEPENDENT chuck, what is the working position? Please compare and contrast with the same concept for a three jaw self-centering chuck and suggest a practical method of setting up your four leaf clover.

Independent chuck jaws (more specifically the faces of the ones under discussion) do not necessarily need to be ground while in the body of the chuck.

21/10/2019 14:01:10
Posted by Hopper on 21/10/2019 12:08:09:

Four thou (.1mm) is not a lot to grind. A dremel held in the toolpost would do the job while the jaws are clamped on a cloverleaf plate to spread them in the operating position.

It's a FOUR jaw independent chuck. Not necessary.

To the OP, have you also checked the other (stepped) side of the jaws as you might need to use this one day?

Thread: How to use CamCalc for cutting Camshafts
19/10/2019 07:56:21
Posted by ian j on 18/10/2019 20:30:44:

C:\users\ian\documents>java CamCalc 128 .075 .562 .1375 1000

CanCalc produces a table of results in 2* increments I really would like 1^ increments but can't work out the command line

I think you need to add -a1 to the end of your command line, separated from the 1000 with a space.

Thread: VFD and screwcutting
16/10/2019 19:50:47
Posted by Clive Foster on 16/10/2019 10:06:27:
The speed adjusting potentiometer in the stop is an interesting idea. What do you see as the advantages over using a simple stop switch and relying on the ramp down of the VFD to bring things to a stop. Obvious one is that it allows you to use a different braking profile for screw cutting / feed to a shoulder than the normal stop ramp down.

The suggestion of an automatic pot to ramp down the speed was an extension of Pete Rimmer's observation that a VFD can be used to back the speed down.

It seems to me that something fixed on the machine that is actuated by the movement of the machine would be more repeatable than the user twiddling a knob. With a human in charge, the start of the twiddling and the speed of twiddle are rather variable.

As to any particular advantage, can I table this for discussion? It may be easier to set up or adjust this form of control: set the carriage in the position you want it to to stop at; slide the control mechanism until it is telling the VFD to output zero Hz; slide the whole switch/control assembly along the bed until it touches the carriage and secure in place.

I think in this way you could get very precise and very repeatable positional control of tool relative to workpiece.

With the microswitch, you have to position the assembly some unknown distance before the stopping point to allow for the ramping and then judge the exact switching point of the switch (clamp it in place on the 'c' of the click and not the 'k'. As you showed in the picture, the mechanism needs to have over-travel capacity in it. The tumble dryer one is an excellent source.

I am slightly concerned about comments on ramping that the time is independent of the speed. So if you have a five second ramp time, it takes 5 seconds to stop whether you are doing 20mph or 200mph. One does not need a seatbelt; the other possibly requires a G-suit to prevent injury.

I also need to think a bit if thread pitch being cut influences the VFD ramping method. Say we can control to 25% of a turn. The distance moved in 25% of a turn is quite different between 4TPI and 40 TPI.

Maybe time for some experiments: set up a dti on the back of the carriage and run into the microswitch at various speeds and pitches and see if carriage stopping position varies.

15/10/2019 18:03:28
Posted by Pete Rimmer on 15/10/2019 13:29:31:

...another benefit is that you can use the speed control to back the speed right down as you approach the shoulder so that the stop is almost instant....

And if you had a sliding potentiometer attached to the bed, you could do this automatically, in a similar manner to the trip mechanism on dog clutches used for screwcutting.

Thread: Chipmaster Motor mounting
15/10/2019 17:50:00

Manual pictures show correct mounting arrangement.

Three of everything.

Vibration pad is just like an exhaust mounting. 1/2" UNC male/female. Nominally 2" diameter. Nominally 1" high. Male bit screws into base, female receives bolt through adjuster.

Tension belts using adjusting screws.

Exact replacements probably hard to find, but 25mm high, 50mm dia. female/female with M12 thread would do and just require drilling out cabinet threads to use bolt inserted from underside and new M12 upper bolts.

Thread: Colchester Chipmaster Part
11/10/2019 21:51:30
Posted by Paul Valente on 11/10/2019 16:35:46:

I’ve actually got the piece down to the base of the taper.

All I really need is an exact length for the threaded portion.

Which piece do you have? The hexagon part that lives in fresh air or the 1/4" UNC part threaded into the headstock? If the part threaded into the headstock through the aluminium cover is not there (i.e. the female threads in the headstock are clear), it might be a good idea to look inside the headstock to make sure it has not worked its way in there.

This is a situation where you will be really happy to see the broken off end of the fastener in the casting.

A countersunk fastener's length is always given from top of head to end of screw so the length of the threaded part itself is not usually given. Your assumption is correct, so what you have to do is determine the countersink angle. I did not tell you this as I cannot remember if UNC is 90 degrees or 82 degrees. Simply remove one of the other screws nearby and copy it.

11/10/2019 14:46:19

Two thirds of it is the same as one of the adjacent 1/4"-20 UNC x 7/8" long socket countersink screws that hold the cover on (including the countersink angle).

So remove one of those to have 67% of your drawing.

The rest of it is a 9/16" A/F hexagon, 7/16" long with a 3/8" diameter groove in it, 0.150" wide.

The remaining 33% of your drawing can therefore be determined by measuring the width and thickness of the semi-circular cut out in the splashback.

Thread: 3 Phase
29/09/2019 07:40:59
Posted by peak4 on 29/09/2019 00:31:57:

Old Mart, there's a little bit more to it in that each of the three windings need to be in the correct orientation...

The motor will run rough and overheat otherwise, as one coil will be working against the other two.

Could you kindly describe or post a credible diagram showing how it is possible to put the windings in an incorrect orientation.

Reversing the ends of any winding is exactly the same topographically as swapping over two wires of the supply. This is the standard method of making the motor turn in the opposite direction.

Thread: Aciera F3
16/09/2019 21:06:48
Posted by Ian Lee on 15/09/2019 22:27:18:

...my question is does anyone know the external dimensions of the collets or does anyone know where I can get a drawing...

If you put in such terms as 'W20 collet drawing' or 'W20 collet dimensions' into Google, you will find what you seek.

Not yet mentioned above as sources are small-lathes.co.uk and www.rcm-machines.com, the latter being very good as they have an ER32 holder on a W20 shank for 89 Euros. They also have a W20 internal thread to M12 adaptor (good start to a drawbar). Should you need a suitable W20 tap or die, they are available from China on eBay, denoted as SV20 thread. For screwcutting, do not be put off by the strange looking thread pitch - think in fractions rather than decimals and gear the lathe 5/3 of 1mm.

Thread: Myford 254 thread dial indicator
09/09/2019 19:57:59
Posted by Philip Slater on 09/09/2019 19:09:58:

I've never machined gears but I've got a milling machine so have the tools. Thinking aloud I wonder if I could machine the gears from Tufnel. Not sure what you mean by having 2 gears, are you saying you need to change gears on the Thread dial indicator?

Do not be alarmed: a thread dial indicator is in no way a precision mechanical device. Almost any kind of tooth shape will work; the important thing being the number of teeth (even so far as straight gashes around the perimeter of a thin gear.

You would do very well to buy Martin Cleeve's book on screwcutting as it probably the most concentrated source of information on leadscrew indicators out there. You can also search this site (using Google with site:model-engineer.co.uk as part of the query string - since the forum search is totally useless) as the subject has been done to death here as well.

Very briefly, thread dial indicators for an imperial leadscrew are very simple because of the way imperial threads are defined (teeth per inch) and one gear will do all pitches.

TDI for metric leadscrews are more complicated because metric threads are defined by pitch. One gear will not do all pitches. However, in some ways metric pitches are simpler because any pitch that is a factor of the leadscrew pitch does not need an indicator at all - you can drop the nuts in anywhere they will engage.

For your 3mm pitch leadscrew, this means 3.0, 1.5, 1.0, 0.75, 0.6, 0.5, 0.3, 0.25 and 0.2 pitch threads do not need a gear. The remaining common ones (especially 1.25 and 1.75) will need an indicator gear (1.25 needs a gear with teeth 'by fives' and 1.75 needs a gear with teeth 'by sevens'.

Thread: wire bender
07/09/2019 16:15:21
Posted by duncan webster on 07/09/2019 16:02:20:

I want to buy a tool, got far too many other jobs on the go to start making one, I just need pointing at where to get it

Put 'wire bender' into Google images. There is one common design that seems to be sold by many people, so make your choice of seller.

If there are many to do, stacking three or more wires on top of each other and pulling the loops all at once will speed things up. This is how small reinforcing bar is bent.

Thread: 4 jaw Self centering chuck recommendations please
03/09/2019 17:12:44
Posted by peak4 on 03/09/2019 10:55:29:

Has anyone seen a vendor offering these with a set of outside jaws included (or even available?)

The only off-brand one I have seen with both sets of jaws is by a seller called niuniucme on eBay. Unfortunately, they are in US but if you have a contact there, it may be of some use.

For brand name ones in UK, Rotagrip are competitive.

Thread: ACME thread identification question.
02/09/2019 20:42:27
Posted by Pete Rimmer on 02/09/2019 14:00:47:

They specified the OD for the blank for rolling the thread on the imperial cross slide screw to 4 decimals.

But could that be because the thread forming process (rolling) is quite fussy in that respect? Maybe if checking using three wires, this is the diameter that gave correct results.

It may be similar in concept to thread forming taps: for success, you need to be a lot more careful in your tapping drill selection.

Thread: Substitute for limonene
30/08/2019 07:49:41

I am not a chemist but...

... is there something different about HIPS that makes standard polystyrene solvents unsuitable? Or are most polystyrene solvents also ABS solvents?

The Wiki page for limonene says it is used in paint strippers (I think one US one is Citristrip). This page might be a guide to alternative sources.

Do some experiments. Put some strands of HIPS and ABS into a few glass jars and fill with solvent of your choice. Come back next morning and see what remains.

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