Recent Posts

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91
CNC / Re: DDCSV1.1 4 Axis controller
« Last post by TurboRexed on September 17, 2017, 07:30:43 AM »
You are buggered Chriscnc, if you cannot change that y axis slightly, the new revision controller is your only fix 👍
92
Project Logs / Re: Spindle problem with cincinnati tool and cutter grinder 2 spindle
« Last post by PekkaNF on September 17, 2017, 07:00:19 AM »
About belts, flat belts and their reliability I should know something.....

But I rather use calculators, because they tell me is something looks about right or misses the mark a mile or more.

So, I streched the original belt over two 25 mm OD electric conduits (sor of like pulleys) meassured the max. distance, streched hand force and youg tape manipulation and got result of 1083 mm, threfore the belt length is about 2195 mm, tried to cross reference that agains information on net.


Used this calculator:
http://best-drive-belt.co.uk//belt-calculator/flat-belt-calculation.html

Bit of monkeying arounnd with numbers to make them sit into actual physical parts and calculator looks like this:

So, I'm thinking of buyin this belt 25 mm wide. What do you think?
http://best-drive-belt.co.uk/flat-belt/flat-belt-det.251202200.html

Pekka

93
How do I?? / Re: Diffusing light within plastic?
« Last post by Mike E. on September 17, 2017, 06:09:06 AM »
For diffusing the light, here is a possible solution. Items needed are....... a black plastic cover from a pen or sharpie marker which would fit over the LED, a cap from a suitable plastic bottle cap cut to fit around the ringer button, and a few fibre optic strands. (possibly from one of those novelty lamps).

1.) Drill tiny holes around the plastic cap and the pen cover  for locating the fibre optic strands.
2.) Punch out the center of the plastic cap and split it to fit around the ringer button.
3.) Feed the fibre optic strands through the plastic cap, glue in place with a drop of super glue from the back side, then cut flush with the face side when dried.

The optical effect should be star like around the perimeter of the button. Here is a rough sketch, hope this helps.



 

94
How do I?? / Re: Diffusing light within plastic?
« Last post by SwarfnStuff on September 17, 2017, 03:14:28 AM »
OR, try (if there's room) putting a ring of opaque / translucent plastic between the LED and bottom of sensor. Perhaps this will diffuse enough light to make the light more even???
John B
95
Project Logs / Re: Spindle problem with cincinnati tool and cutter grinder 2 spindle
« Last post by PekkaNF on September 17, 2017, 02:37:24 AM »
Thank you.

I am electrical engineer, but I have been tinkering with machines all my life. At one point I was involved in servohydraulics and mechanical maintenance. It is diffenet to follow guidelines and practices or design something new. This is something old and obiviously clearly successfull design that I can't rebuild (blueprit) with original parts, I have to get a little creativive with different rpalacement parts that went in originally.

I know a little of some things and when I try to do something rather new to me, I try to learn enough. But at the very begining of learning curve it is really hard to find out what is essential and what is not and some information you get it wrong or not really usefull on the application you have at hand.

Like lubricant and clenliness. Someday it is rally not that critical, and on some systems it is laa important.

I'm prepared to wash all parts, dewater, lightly oil, use lintfree cloth to clean all critical surfaces and use clean good quality grease fron new tube. But I'm not going all grazy about filtering all liquids, air and grease.

This assembly is a bit tricky: There is no provision for removal of the bearings from IR, therefore have to get them right first time. Both ends are removed by pulling the bearing from OR and that transmits the extraction force wrong way: OR->balls->IR and the IR is mounted with light press fit, this could mean brinneling the bearings.

So I have to mount bearings to shells, calmp OR very lightly to keep the bearings in place and then press bearing IR to shaft using a fitting bushing. Will need to "dry" run the thing without bearings, to make sure I have all bushings and pads ready before I start the work.

I have to measure the belt carefully. Looks like I can't order the te belt and bearings from one place, so postage will add up a little.

Pekka
96
Project Logs / Re: Liquid Fuelled Rocket Engine
« Last post by PK on September 17, 2017, 01:25:47 AM »
Did I miss-read or are those calculations just for the throat section of the motor?
The throat is the hardest part to cool, but it's not the biggest source of heat. Particularly in a development motor where you tend to run conservative (read big) L* chambers.

Re strength. If you make the cooling jacket and saddle (I'm assuming you're doing it that way) such that it can take some load, then you can run thinner chamber walls and get better heat flow.

One important point, and I assume you are doing this. I know of no biprop that doesn't rely on film/boundary layer cooling. If you push your rich mixture to the edges of the chamber you can pull 300deg out of the combustion temp near the walls and still get reasonable ISP because the rest is nearer to stoichiometric.
97
Project Logs / Re: Spindle problem with cincinnati tool and cutter grinder 2 spindle
« Last post by gerritv on September 16, 2017, 08:37:29 PM »
Very methodical and for me educational. I won't fear my eventual spindle bearing replacement as much as I did before.
98
How do I?? / Re: Diffusing light within plastic?
« Last post by PK on September 16, 2017, 08:06:16 PM »
Assuming that the circuit will go in a box. Try using two or more leds NOT pointing up at the plastic ring. Make the inside of the box as reflective as you can.  When you are staring at it on the bench it won't seem bright enough. But in place it may well be fine..

Worth a try I reckon.....

PK

99
Project Logs / Re: Liquid Fuelled Rocket Engine
« Last post by British Reaction Research on September 16, 2017, 07:49:00 PM »
Hi Bill,

Thanks for replying and thanks for wading through what I had written. If you were to re-read it with a view to commenting on my approach to the problem then that would be most gracious of you. I would be very grateful indeed.

The boiler economiser you have designed sounds very interesting indeed. I seem to have found the right person to look at my results!

I'm planning on using a gas pressurised feed for the engine, at least to begin with. Some other calcs that I've done to determine the Reynolds number indicate that even with an annulus type parallel flow coolant gap in the jacket of 5mm - easily achievable - the Reynolds number would be in excess of 127000. Anything above 10000 in liquids and you have turbulent flow.

As I mentioned one plan I have is to use cross flow - the coolant flowing perpendicular to the axis of the nozzle. This would induce even greater turbulence and vortex generation, all of which are good for heat transfer. Knurling or milling grooves or slots in the nozzle outside wall would also induce turbulence and eddies, as well as becoming nucleation points for a boiling heat transfer regime.

I think that one thing I didn't mention in my above post is that the numbers would be for steady state operation. As the rocket engine is likely to be run for short durations it will probably never attain steady state conditions.

Another point I forgot to make is that the engine ought to be tested with water as a coolant to begin with. As is well known, water is a formidable thermal fluid and will easily cool the nozzle and chamber in the way described in my post above. The inlet and outlet temperatures can then be measured and from that the performance of the cooling system can be checked. Only when it is proven as safe will I try to regeneratively cool the system with the fuel.

Thanks again for taking the time out to read my post and to comment on it.

Carl.
100
Project Logs / Re: Liquid Fuelled Rocket Engine
« Last post by billmac on September 16, 2017, 04:47:11 PM »
Carl -

That was indeed very interesting. I will need to read through it a few times to get the full picture.

You seem to have quite a bit of headroom in the coolant temperature increase. As you state, for good heat transfer you must have guaranteed turbulent flow - the difference netween that and pure laminar flow is large. Are you using a pump to deliver the fuel or just gas pressure in the fuel tank? If pumped, can you recirculate fuel?

I have recently gone through some heat transfer calculations to design a boiler economiser. In that case we had the luxury of using a more powerful pump and re-circulating the hotwell contents. The end result was a significant increase in boiler performance and a fast recovery rate from heavy steam usage.
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