Member postings for Tim Taylor 2

John,

Yes it will export:

1. Open the part
2. click on the jewel in upper left corner, then new/new drawing to create a 2D drawing
3. select the drawing parameters and views to create the drawing - you can edit or add additional dimensions at this point......
4. click on the jewel and click on export to export to common CAD format (DXF or DWG)

Edited By Tim Taylor 2 on 21/01/2019 16:17:05

Yes, just make the change, exit 2d sketch mode, then click on regenerate to last feature....any subsequent feature affected by the changed sketch will update automatically.

This is one of the capabilities of A3D that can be a huge time saver. 

A good example is the design of the turbine wheel I posted back on page 23. Getting into the nozzle flow calculations, I found it necessary to increase the blade area by 50%. This involved three changes:

1. edit the sketch for the extrude buss of the rotor OD
2. edit the sketch for the extrude cut for the reversing sector clearance
3. edit the circular pattern to reduce the number of blades in the row by one to provide necessary blade to blade clearance.

Three simple edits that only took a couple minutes....then hit generate to last feature to create updated design.

Edited By Tim Taylor 2 on 21/01/2019 15:58:40

1. My preference

2. OK as well

3. No

The only thing I use color on 2D drawings for is revisions, and those are in red - makes it easier to quickly see what has changed.

I do like the small isometric.

Edited By Tim Taylor 2 on 21/01/2019 07:19:43

I'm jumping in a little late as well.......a couple things:

The combustion air on any boiler should be adjusted for proper fuel/air ratio - excess air improves combustion, but too much can dramatically increase the stack temperature and reduce thermal efficiency. On full scale boilers, on gas fire, we target for about 3% excess O2, which translates to about 15% excess air.

I'd probably also fit a simple superheater coil - easiest place to add it would be right at the stack....

Tim

Edited By Tim Taylor 2 on 20/01/2019 22:41:42

TG,

That answers my question.

Regarding efficiency, I think you have a couple things going on that may be throwing you a curve.

First, there is a big difference between D&S steam and compressed air - steam has roughly 8 times the enthalpy of compressed air at the same pressure & temperature. Steam is not an ideal gas, and steam engines are designed to take advantage of the isentropic enthalpy drop and the expansion characteristics of steam. The valve timing for steam, for example, is not what would be the most efficient for compressed air. A steam engine running on air will not be as efficient as if it were running on steam.

Second are the leakage paths you have already mentioned. Design clearances take into account thermal expansion at operating temperature, and what may be a significant leak at room temp, will not be at designed operating temperature.

Was your clearance volume in in^3 or cm^3? Based on your 14mm bore by 18mm stroke, I calculated the swept volume as 2.77 cm^3. The optimum clearance volume is typically around 10% of the total volume, so if your clearance volume is in cm^3, then it's in the ball park.

I find your progress quite interesting - please keep us posted.........

Tim

Edited By Tim Taylor 2 on 20/01/2019 22:13:48

sorry....16 watts.....

TG,

Might be a stupid question, but is your 20 watt estimate based on compressor input power or net output? Compressors are notoriously inefficient, typically 50% or less - a lot of the energy is lost as low grade heat from the heat of compression.

Tim

TG,

Pic below is what the machined rotor will look like prior to adding the buckets & shroud. I will likely model most of the major parts on my 3D printer to make sure I have things correct before I machine anything.

I am having a similar issue to yours in that the buckets are small and tolerances are tight. What I'm currently playing with is forming the blade from 0.025" flat brass stock in a press using a die. It would be roughly 0.050" wider than the final dimension, with the excess width machined off in the lathe after assembly, this would also provide the desired sharper edge on the blade. I need 80 of the blades for the wheel and another 8 for the sector.

Copy & paste it into your browser - it is a link to Allied's criterion boring head technical specs for all their products

Hi All!

I am working on a design for a scale model Curtis type turbine - it will have a 3" diameter 2-row wheel with reversing sector. The screen capture below is of the wheel design using Alibre Atom3D. The rotor body is a dish design, machined out of a single piece of metal. The buckets will be individually formed, silver soldered into slots in the rotor, then the shroud soldered to the outside. Once assembled it will be trued to final dimensions on the lathe.

reversing sector

casing cover

Edited By Tim Taylor 2 on 15/01/2019 19:46:21

Edited By Tim Taylor 2 on 15/01/2019 19:49:26

take a look here:

https://alliedmachine.cld.bz/Criterion-r?v=11519135013

Tim

Jason,

While the concept used is not new, the way EE has designed the Turnado is pretty slick.I particularly like the way the tool holder is designed - with the front of the supporting foot well in front of the tool all the force is directly down and there is very little chance of the work grabbing the tool and flinging it somewhere. Also, the rake angle on the tool should be neutral (0 deg) for the same reason. With minimal additional fixturing you could turn some pretty accurate and repeatable decorative shapes, tapers, etc.

I have seen videos where a conventional tool is hand held on a riser block for doing free hand machining, and I think the Turnado idea is much safer.

The only real drawback for me is that EE is located in Australia, and the shipping costs to the US would be prohibitive. They sell the tool holder as a separate item, and I might just order one of those - the rest can be easily fabricated from raw materials obtained locally

Tim

Edited By Tim Taylor 2 on 15/01/2019 15:36:28

Neil,

Might work with a single row wheel. In the design I posted above the clearance between the 2 rows of the wheel and the reversing sector is only 0.025", so you would need to really open it up. Also, the buckets are relatively small - roughly 0.2"x0.2"x0.15" - pretty small for a 3D printer....using fewer, larger buckets would probably work.

The disc and hub for my design will be machined out of a singe piece of steel. The buckets will be brass and silver soldered into slots in the wheel, the rim soldered to the buckets, then machined true. Right now I'm working on the best way to make the buckets, and I'm getting closer (in the real world they're done out of SS on a broaching machine).

Tim

Yeah, I figured out what I needed to make it work. Part of the problem was that i was focused on creating the extrusion at the final radius, then it dawned on me that all I had to do was create it at the origin, extrude to the final radius, then extrude cut what I didn't want.

Rather than using multiple steps to shape the bucket as I did originally, I created a sketch of the final profile, then simply extruded it. Both rows of buckets on the picture I posted above were created simultaneously by one extrude boss, followed by one circular pattern.

I've only been playing with the software off and on since mid-December, but I think I'm starting to get a feel for it. IMHO the integral help is good in some respects, but in others is only enough to make you dangerous. I've kind of filled it in by playing with it, and also tips found here, on the Alibre forum, and some Youtube vids.

Tim

I was able to consolidate some operations - this is the 2 row Curtis stage wheel design with a dished rotor..........

Awesome John!

I think I'm starting to get a feel for the A3d software. The picture below is a single row wheel for a steam turbine - I did it as a learning tool...the actual scale model turbine I am designing will have a 2 row wheel with reversing sector.

The most tedious part was figuring out the bucket design - it starts out with an extruded rectangular block, which is then shaped to profile by a couple of extrude cuts. The circular pattern was used to create the buckets in two steps - first the rectangular blocks, then the extrude cuts using the same parameters. I did it this way because as far as I can tell, the circular pattern will only work on one feature at a time.

The wheel body was a couple of extrudes and very straightforward.

The rim was created separately and then projected to a sketch, which was copied and positioned on the wheel using the paste stamp function, then extruded to width.

I did this early in the week, and in retrospect it looks like there are a couple of steps that could have been combined - will play with that when I get a chance.

Tim

Nope, I missed using the tangent slope function. We got the same result, but your way is simpler.

Thanks,

Tim

David,

I think what Tom is after is something like this pic (transparency set so hole is visible)

2 thru 6.......can't type tonight....

My bad - the above will create the hole at an angle relative to the tapered surface. Creating relative to the cylinder centerline is easier. If you draw the center around the origin, then the first step is to create a plane parallel to and offset from the vertical axis that passes through where the center of the whole will be....then follow steps thru 6.....

Tim