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  1. Dougt115

    Help! Need a simple way to analyze some data.

    What are you calling a plenum? with a single inlet? It sounds like you installed a sawdust collection chamber with a single inlet to create the flow? Is this under the floors or along the walls or at the machine throw area? My first take is that your model complete missed the effect of the...
  2. Dougt115

    Heat gain/loss in building? Trying to spec insulation. Building wraps? Spray foam guys are nuts!

    Spray foam is R6 per inch while fiberglass is R2.2 per inch or about 3:1 ratio. So about 7 inches of foam will do the job to reach a R40 while almost 20 inches of fiberglass will be needed.
  3. Dougt115

    Mechanical Engineering Student/Intern

    It is not the complaints it is the reason for the complaints. We had a part designed from 4140 with a 16 finish, the machinist hated it because it was gummy, had to be sent out to be hardened and then ground. I listened, reviewed the part and changed it to 17-4. It may cause more wear on the...
  4. Dougt115

    Mechanical Engineering Student/Intern

    If you want to get your hands dirty look for jobs in the smaller companies that manufacture in-house. Mechanical Engineers in big companies don't get to get dirty and spend a lot of time on the computers. But small companies you have to get the job done and that means getting on the floor.
  5. Dougt115

    Plain Tubing Vs. Fin Tubing

    Unless you are making the finned tube yourself the manufacturer should have the information you want. It is a selling point to convince you to buy his product after all.
  6. Dougt115

    Doubling the air flow-rate across an evaporator coil

    These theoretical discussions are great but So Cal does not have a humidity issue unless you are on the coast or don't vent your shower and often it is too dry. Also if the air flow is too low now (sub-optimal for the ducting) then doubling it wouldn't likely cause any of these issues...
  7. Dougt115

    Doubling the air flow-rate across an evaporator coil

    The temperature drop from input to output of the heater/cooler would be less. Just because the heater/cooler has less time to interact with the air. However twice the air would pass through Your current system may drop the temperature by 2 degrees at a rate of 600 cfm. Your new system may...
  8. Dougt115

    Corner pitting after pressure test

    I don't see the spalling. I see cracks. Was it pitting? Did material come off? Do you know which nitriding method was used? Gas, Salt bath or plasma. The location of the pitting (also looks like there are cracks between each pit) is in a transition point from one diameter to the next. This...
  9. Dougt115

    Unconstrained motion in hamiltonian mechanics

    As complex as it may be I don't see a better option than the Center of Mass as a reference. While it is true that it is not connected to any single point on the system it is the only point that is stable. The bars in the linkage will gyrate and move in complex patterns but the center of mass...
  10. Dougt115

    Balcony Collapse in San Francisco

    It looks like the balcony ended up upside down on the lower balcony with the side that was facing the door now facing out. And part of the floor still attached to the original floor, this makes the balcony look like it has no floor anymore. So the balcony rails let go of the building and the...
  11. Dougt115

    Drilled holes in hollow rotating shafts in mixing application

    Vent holes? Is the room temperature to mixture temperature large? Would the pipe deform due to internal pressure?
  12. Dougt115

    Mechanical seal failure flow rate calculation

    Define fail. Your valve is 100% functional to 100% failed. You could calculate the flow rate without seals to determine max leak rate. Then you will know you will be between this number and zero.
  13. Dougt115

    Drilled holes in hollow rotating shafts in mixing application

    If it was to prevent floating then it would have to let the mix in. This could cause the material the enters to not be properly mixed and ruin any chance at a uniform mix. Guessing it is not for floating. A pipe of this size, length and slow speed would be for large volumes and high torque...
  14. Dougt115

    Drilled holes in hollow rotating shafts in mixing application

    What is the mix? Liquid, gravel...? Could be used to mount a sensor that is no longer used? Doesn't the mix get into the shaft through the holes? Drain hole?
  15. Dougt115

    Help with building a lift table

    Guessing you want this to be your project or as mentioned you could just buy one. Here are a few safety issues to think about: 1) Stability, either a wide base or bolted to the floor. 2) Plenty of overhead room. 3) Access ramp to get the bike on the ramp. Don't expect to drive it on or you may...
  16. Dougt115

    question about spline design

    The 80 MPa is the calculated stress, the 35MPa is his stress limit for fatigue. He never said what the material is. But steel should be closer to 30Ksi and higher. These stress levels sounds more like a plastic or ceramic than a metal. The fatigue analysis should be giving you the stress...
  17. Dougt115

    Materials Touch Temperature

    VAR10 Thanks for the added information. How about making the touch points removeable so that they don't go in the oven? Make the handles of the clamps so that they can come off quickly. Put the part on the fixture, tighten down, remove the parts the technician touches, place in oven. When it...
  18. Dougt115

    Spline Shaft Extreme Wear Help????

    Miss-alignment would allow an axial force that could result in your gear moving up or down during operation. The wear looks to be caused by the retaining ring itself. Check the hardness of the gear compared to the retaining ring I wouldn't be surprised if it was either much softer and/or...
  19. Dougt115

    question about spline design

    From what I have been working on. Fatigue is an issue. The 2x is a design margin and may not be enough depending on your loading and material. You can get SN curves for most materials. The curves are not application specific so you may need to test to verify it meets the requirements...
  20. Dougt115

    Materials Touch Temperature

    A little more definition is needed. I am assuming you need production to be able to remove the unit from the fixture soon after exiting the oven? And then reuse the fixture for the next unit to go in the oven? What are the features of the jig? Is it a cookie sheet or a holding fixture? Does...

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