Member postings for Trev67

Hi Rupert

where in London are you, if you are SW then I may be able to help.

Trevor

Hi

I built one of these a few years ago. I'll dig it out and take a photo when i get a chance. I used a piece of 4" black plastic tube for the displacer cylinder, the studs holding the plates together I made of stainless to reduce heat transfer.

I didn't like the way the crankshaft was all overhanging one side, so I altered it and put the power cylinder on the flywheel end.

good luck with you build.

John

Thanks for explaining it, I do kind of understand, but not to the extent that I could come up with the design myself.

It was only when I look at the data sheet I realised that the two op amps are actually in one component, so I see what you mean about it being a no brainer to use both.

When I get this up and running I'll report back. I did find it very frustrating when trawling the web for answers that many forum threads, just die out without reaching a conclusion.

Thanks everybody , especially John

Regards

Trevor

Hi Martin

You could contact the boilermaker and ask, if they say it is ok to cut the welds back then get them to put it in writing, if it is not ok, then the boiler is unfit for purpose because it doen't fit, so I would then send it back.

good luck with the build

Trevor

Hi Brian

My manual definately states 4mm pitch for the metric machine. all the other information I have is for the imperial one, metric threads being cut with the aid of a 127 tooth changewheel.

Trevor

Many thanks John, thats what I was hoping for. I guessed the original circuit was on the right lines, but would need tweaking to work with the different voltage. Now to get it built and see if it works!

Thanks to everybody who has contributed to this thread, my electronics knowledge is not very good, some of the discussion is over my head. However I've tried to follow it and learn a bit more.

If anybody would like to explain in simply terms how this circuit works and how the design is arrived at I'd like to know. I know what PWM is and resistors and capacitors, opamps are a new on me so it's a bit of a learning experience.

Neil, why not a single comparator? I havn't got a clue, it's all way over my head, perhaps you'd like to explain the circuit and come up with something simpler that would do the job?

Thanks again

Trevor

I'm pretty sure the voltage is no 0 -10v

I am measuring the voltage with the motor running, across the outer two terminals of the pot there is 3.7v, if I measure the low side and the centre I get between 0 - 3.7v as I move the control. This seemed strange to me as I was expecting 0 - 10v. The only other reference to this control board I could find on the web was someone on another forum who had one on a Starmill. The thread died out just after the poster was being told about 0 -10v, maybe he dissappeared in a puff of smoke!

I do have a SpindleV5 board from diycnc, but I have two issues, the output is just two terminals 0v and 0-10v, so I'm guessing that it would make my motor run at full speed from 1/3 upwards, and the extra voltage could damage the motor controller. The other problem is that it uses the A axis step signal to control the speed instead of PWM. This is more difficult for a novice like me to configure in linux, so I'm thinking that it is not really suitable.

If the original circuit that I posted is not suitable, I found others in this post on the mach forum**LINK**

Could one of these work but with a 5v power supply?

Thanks for you help

Hi,

Thank you to everybody who has replied, I'll have a look at the links.

Here is the circuit I was refering to in the original post. I was hoping this might be suitable for a number of reasons:

1. The input is a PWM signal, this is easy to set up in linux, I do have a spindle control board, but it uses the A axis step signal, and this is trickier to set up in linux (easy in mach 3 I think).

2. The 10v and 0v are derived from the motor controller, so if these are 3.7v and 0v will it still work and give me a proportional voltage to control the speed.

3. This circuit appears to be isolated, so if I have got a floating voltage on the control side of the motor controller, then it should be ok.

4. If the 3.7v isn't enough to drive this control circuit , is it possible to alter the values of some resistors to make it work, or even supply it with an external voltage to power the circuit, without affecting the 3.7v on the output. ( I have 5v and 12v available from the breakout board)

5. The commercial boards all seem to work at 0 - 10v, I'm concerned that it will either run at full speed most of the time, or possibly damage the motor controller.

I hope the picture is visible, It was a .png file, I had to invert the colours, and save as a jpeg, so it is a bit feint.

Many thanks

Trevor.

Hi

Could get the circuit diagram onto the posting I think I managed to save it in my album as a jpeg, hope its possible to see it.

Thanks again

Trevor

Hi

I have a Denford Starturn 8 cnc lathe that I'm trying to get working on linux cnc. I have the axes moving and spindle switching on and off, I would like to get the spindle speed under computer control as well.

The speed controller is a JAY JE124/1. It controls a 160v dc motor. It currently has a manual pot to control it. I know about the issues of the control side not being earthed and having a floating voltage.

I've seen lots of references to these controls having a 10k pot and 0 -10v to control the speed. Taking some measurements it seems like my pot is 3.5k and the voltage across it is 3.7v. If I check the voltage from the pot terminals to ground, I get strange readings, so I assume this is floating, and needs to be kept isolated.

I've found a circuit diagram which I will try to add to this post, it's by John Haine, who seems to be on here, so John if you read this, you may be the man to help.

With reference to this circuit, it appears to be isolated, so that is good, also the voltage it is controling seems to be derived from the speed controller, so if it is being supplied 3.7v instead of 10v will I get a 0 - 3.7v control, or will this not be enought to make the circuit work.

My knowledge of electronics is very limited, all I know is if you let the smoke out it doesn't work, so if somebody could advise on this circuit I would be very grateful.

Thanks in advance for any help, and thanks John for producing the circuit diagram in the first place.

Trevor

Hi Mike

I think lighter fluid, the type for Zippo lighters works, and it's a bit quicker drying than white spirit. Obviously try a small amount first before committing.

Hope this helps

trevor

Hi all

The question of new technology, and whether it should be adopted and whether it is cheating has cropped up over and over again.

Consider this:

In LBSC's day with limited equipment many would buy, say a loco frame stretcher casting, file the ends square drill and fit.

Nowadays maybe you would draw it in CAD, get it laser cut, braze together etc, or maybe model it in 3D CAD, write code maybe with CAM assistance, set up and CNC machine it from solid.

or another case:

Buy a wheel casting, machine and fit

or

Model in CAD, CAM and CNC machine from solid.

Who made more of it themselves?

Staying with locos, what about laser cut platework and frames, ready made boilers, lost wax castings etc.

The perception that cnc isn't skilled or isn't your own work seems to be a fallacy, especially when the hobbyist may have built or converted the machine themselves, learnt CAD, CAM, G code and how to set the machine up.

Anyway each to their own, and it's better to be making stuff or learning something than watching deadenders all evening

Trevor

Hi

I know very little about electronics, so be gentle with me.

I'm converting an old Denford Starturn 8 lathe to run from a PC, haven't yet tackled the speed control, it currently has a manual pot to control it. Whilst trawling the net for information I have come across warnings that the control side of old speed control boards is not grounded and floats at up to 100 volts, so it may be that there should be a floating voltage at the pot terminals. As I say I don't much about electronics, but thought this could be helpful.

I've not investigated mine yet, but obviously interested in the solution to controlling these old boards.

My speed control board is a JAY JE 124/1, and controls a DC motor, if anyone has any useful info

Good luck with your projects, and happy new year to you all

Trevor

Hi Brian

The leadscrew is 6 tpi.

I'll email you some pictures, hopefully they'ii be usable.

Trevor

Hi Martin

2804 are the collets for a Smart & Brown model A, I think they also fit the model L plain turning and capstan lathes, I don't know about the others. The ones for my Model A are all marked 2804. I think they are a specific collet for these lathes, slightly bigger than a 3C and smaller than a 5C.

The sizes will be imperial, the 25mm diameter is 63/64 which is the spindle bore, the thread is approx 0.9" diameter probably 29/32, and 24tpi RH.

Hope this helps

Trevor

Hi

Do you have 25 tpi on the gearbox, if so select change wheels to speed up the gearbox input 2:1 and use the 25 tpi setting.

Trevor

Hi Ian

Sounds like you need the equivalent of a leak down tester, used on engines to test for cylinder leakage.

Basically it is an orifice ( in the case of cars they use 40 thou) with a pressure gauge either side.

If you plumb the tester in at A in your diagram, and there is no air leak or flow both gauges will stabilize to the same value, the more flow the greater the difference in the gauge readings. So if you can either turn off all the valves and open one at a time to find the greatest pressure drop, or have them all open and shut off one at a time to find which one makes the biggest difference.

If you have no idea what size restrictor orifice to use between the two pressure gauges, you can put a shut off valve in, and use a bit of trial and error to get a meaningful reading.

Because it is only a comparison tool there is no need for absolute accuracy or calibrated gauges, you are just comparing the flow through the machine against the flow through the restrictor, and if it is significant it will show up as a pressure drop.

Hope this helps

Trevor