Posts Made By: David Hakenewerth

April 29, 2002 02:15 PM Forum: Telescope Making

Mirror Grinding

Posted By David Hakenewerth

I am machine grinding my first mirror and I need some help. First let me say that the process makes a lot more sense when you do it instead of read about it.

I made a dental stone tool about 70% of the mirror diameter and it was working fine but I now think I placed the tiles to close together because after grinding through 320 some of the channels where getting flush with the tiles. I was opening up the channels when 1 tile come off. Now what should I do? Use the tool with a tile missing, Re-epoxy the tile in place or make a new tool. I cast a new dental stone tool about 5 days ago that I was going to use for a pitch lap and it is cast with the correct ROC I could use this for a new tool probably in a day or 2.


Thanks for the suggestions.


Dave

July 7, 2002 01:29 AM Forum: Equipment Talk

12 inch report

Posted By David Hakenewerth

Mark, Congratulations on the excellent results. That 12 incher kinda surprised you on the amount of time required.
do you think if you started offering this size that you could reduce the production time or is your report a pretty good estimate of the required time? Did you do 35 hours of attended polishing or will the machine run unattended at all? I don't think I would attempt unattended operation unless the slurry addition was automated and proven over a long period of time.

Once again congrats and since my loggin shows a different name sign me

Dave H.

July 16, 2002 06:35 PM Forum: Telescope Making

Mirror testing

Posted By David Hakenewerth

I am working on figuring my 10 inch F5 plate glass blank and I have a few observations. I was using the Ronchi test for surface figure and I still have some work to do to get the surface smooth but am very close based on the sessions I have done so for. It shows my mirror is within the 1/4 wave figure based on the Ronchi criteria so I went to the knife edge test to get a better read. I am using the Stallafane design of slitless moving tester and total movement for the 5 zones I am testing is a total of .108 inches and the central 2 zones require a very small move. I can get a pretty good parabolic shadow at the 70% and edge zone but the central zone does not pop out like I would like to see. Also the "expert eye" required to distinguish between the gray scale values is much harder than I thought it would be. I was concerned that my testing technic was weak so I put a commercial 8 inch f6.25 on the stand which has given me decent performance and I was not impressed with the shadow results I saw. Actually my mirror gave closer to the desired shadow results than the commercial mirror but the commercial mirror was smoother in surface smoothness. Actually it was very smooth. I realize now that I need to put some serious time into using this tester and recording data. Those of you experts who can read this test to the 1/10 or 1/20 wave have my greatest respect.

Can anyone point me to a web page or a software program which simulates knife edge results so that I can sharpen my skills. Also any suggestions which would improve my testing methods would be appreciated. I am going to redesign my tester this week to use a dial indicator and make the lateral and knife edge movement smoother so I can set it and study without worrying about any drift. Also I am going to get a better testing tunnel set up so that all drafts are reduced and I am sitting at a more comfortable level. Does it matter if you resetup the tester and stand for every test because right now my testing area is not in a secure location and I have to breakdown and resetup for every test.

Thanks again for the help. I feel a great mirror is right around the corner. shocked)


Dave H.
Dave

July 19, 2002 05:19 AM Forum: Telescope Making

Ronchi testing

Posted By David Hakenewerth

I am redesigning my knife edge tester to include a different
light source and a Quick Cam VC so I am using a make shift Ronchi tester for now. I use RONWIN20 to generate the Ronchi simulations for my parameters at the standard offsets
-.3, -.1, .1, .3, .5, .7 inch. When I look at the actual versus the expected at these zones I get the following results. I started at zone .7 outside the COC and moved inward. .7 was my matching point and I had to match 1/4 wave over corrected because thats as close as I could get.
Zone .5 1/4 under corrected
Zone .3 a little more than 1/4 under corrected
zone .1 looks good
zone -.1 looks good
zone -.3 1/4 under corrected

I'm not sure how to translate this into surface info. I think my mirror is close to 1/4 wave but now I want to try to improve zones on the mirror. Do I need to get my Knife edge back in service or does this Ronchi info give me surface zone information that I can use to continue figuring.

Sorry for the newbie questions but I can find what I'm looking for.

Thanks Dave

July 23, 2002 03:07 PM Forum: Telescope Making

Final Figuring Fun

Posted By David Hakenewerth

I redesigned my Foucault tester by using a Large bright green LED and this did make it much easier to judge the test results. I am using a 5 zone mask on a 10 inch mirror and because of the lack of eye relief I have a hard time seeing both windows at the same time on zones 4 and 5. So I have to adjust my eye position to make this determination. Is this going to skew my observations significantly?

I think I've made all the typical first time mistakes. I have a good smooth surface and I'm within about 1/2 wave right now but I,ve gone through many beginner mistakes to get to this point.

My progression is like this.

A. Central Hill with Raised ridge at 70% zone and slight TDE
B. Central Hill with Raised Ridge
C. Raised Ridge at 70 %
D. Poured new lap and temp in garge changed from 85 to 70 degrees. Now I have blown a large hole and have a depressed ridge at 70% (did this on the machine instead of hand)
E. Center zone and zone 1 blended together and hole removed.
F. Center zone and zones 4 and 5 all need reduced

This is where I am now. In addition I've seen and learned alot about surface defects. Pimples, Dimples, zones, etc.

Most all of the stroke info, lap masking, and eccentuated pressure have work exactly as advertised but one area that is not discussed in much detail but has a big effect in my experience is pitch hardness and flow. I was right on target to produce a nice parabola when I made a new lap and the temp changed which made the lap characteristics much harder. The lap still performed as expected based on the technique but the rate at which this change occured was an order aof magnitude greater. This change in flow increased the laps effectiveness significantly. I blew way past my intended target with a session about 1/2 the duration of the previous sessions. I was trying to be cautious because of the new lap but still was to aggressive. The temps are back to normal now and the lap is back to its original pace.
Slow and steady. I had a productive session last night and hope to test at lunch time.

The challenge just adds to the fun.

Dave H.

July 31, 2002 07:08 PM Forum: Telescope Making

Ronchi Screen

Posted By David Hakenewerth

Some one asked me to print them a Ronchi screen on a transparancy for them and I can't find the gif file I used to use. They normally have one on the stellafane web site but it is out of service until August 10. Does someone have a 100 LPI file I can use to print out some screens for this ATM. I'm not used to Photoshop etc and I know the size and spacing is critical so I would like a known good file. I have access to a 2400 dpi proofing printer and work that can develope on film that makes nice screens.

Send me a reply and we will exchange offline.

Thanks Dave

September 13, 2002 07:09 PM Forum: Telescope Making

Pitch Laps

Posted By David Hakenewerth

I have been working on completing a 10 inch mirror and I had to repour my pitch lap. I added some solvent which has made the surface to soft. My lap is on a dental stone. Is there any way to evaporate some solvent from the pitch on the stone or will I have to remove the pitch and boil it off?

November 8, 2002 08:05 PM Forum: Telescope Making

Newt Software

Posted By David Hakenewerth

I have been using Newt to play with the parameters for a 16 inch truss tube scope. I have the rocker box, Mirror box, Mirror cell and the secondary cage all complete but now am looking at changing the F- ratio to make completion of this self figures mirror easier. I have a 16 inch blank and a 3 inch secondary diagonal mirror and originally I was looking at about F4.75 but now I think I want to go about F6. This changes the 100% illumination diameter and also causes vignetting of the 75% illumination at the enterance and the focuser. I can't really see this as any big deal. Currently the mirror blank is hogged to F6.5 but I have a long way to go to completion. What am I missing.

Thanks Dave

January 1, 2003 10:28 PM Forum: Deep Sky Observing

Jupiters detail and seeing conditions

Posted By David Hakenewerth

I have been trying to duplicate some spectacular views I received of Jupiter on superbowl sunday 2001. I have yet to get close and have to admit that I am still a newbie and have spent much more time in contruction than observing but I want to recapture that night. I live in south central US and have decent dark skies. I have an 8 inch F6.25 and usually view at 195x or 267x. Does anyone know what the normal rating for seeing is in this area. How often do we get good and great seeing? How good does the seeing have to be to get alot of detail with Jupiter? I think I just got real lucky that night and my colimation was perfect. Think I need to work on that some more.

Thanks for any insight

Dave

January 10, 2003 11:03 PM Forum: Religion

Values, Morality, and Culture

Posted By David Hakenewerth

I am not a religious evangalist; however I wish to pose a question. I am concerned about how the lack of concern for our country's religious foundations is affecting our culture. The last 40 years of human rights movements and the seperation of church and state has left a void in our cultural training that was previously taught in the schools. I love America's freedoms and I respect the agnostic and atheists rights to there beliefs; however with religion removed from the schools and the government there is no organized way for us as a society to teach basic human rights. Morals and values which in previous generations were taught as absolutes now are subject to ridicule and debate but nothing formal has taken its place. I see this as a very big long term problem.

Dave