Here is a list of all the postings John McNamara has made in our forums. Click on a thread name to jump to the thread.
|Thread: CRT Free!|
Drill a hole in it!
|Thread: Machine alignment using low cost electronics|
|Thread: Equity release!|
I think the first consideration is the math on life expectancy, According to the UK census at a current age of 70 the average life expectancy is another 14.77 years as of the last assessment made a couple of years ago. This number is the average only, many people beat the average a few by decades.
I think any plans for the future need to take these statistics very carefully into account.
Being caught short a a vulnerable state of age when planning could have avoided it is a very unsatisfactory state of affairs.
|Thread: Machine alignment using low cost electronics|
Thanks Michael I responded with an email.
I Bumped this post because there are some worth wile changes.
There is an executable version available, A Jar file so you will need the current version of Java installed.
Edited By John McNamara on 27/08/2019 01:32:56
"Now for the exciting part; Hidden at the bottom of the Gaussian graph there is a tiny numeric value, It followed my indicator movement when I moved the slide. very roughly a value of 1 to 4 on the graph value to 1 to 4 ticks on the 0.01mm indicator. I assume this correlation may not have been planned however with the particular camera I used it was very convenient.
There is an error in the scaled value that needs to be explained. The dial indicator readings and the values on the screen correlated and were repeatable.
The colour image is converted to grey-scale by the software.
I will keep working on this project.
Edited By John McNamara on 24/08/2019 12:59:40
Edited By John McNamara on 24/08/2019 13:06:43
I stumbled upon the following post on another UK forum.
"DIY laser leveling using webcam and laser level."
The poster provided a link to the software source code on Github
I obtained repeatable accuracy of 0.039mm (.0004" and I am sure that can be improved with a better setup....... remarkable.
|Thread: Hieroglyphics on a Wehlen & Co clock face|
I know that modern watch faces are often Pad printed. (As well as billions of bottles and the like) It works well on curved surfaces.
I also read somewhere that this process goes back 100 years?
|Thread: Black Oxide coating|
One of my treasured books.
Howe does an outstanding job describing formulas on metal and wood finishing.
|Thread: Colchester Bantam gear spline profile?|
My first lathe was a vintage Colchester it was a version of this one. I was very sad to let it go due to lack of space.
The flat belt driven black japan finished lathe second photo down. **LINK**
Edited By John McNamara on 09/08/2019 09:44:16
|Thread: DIY Epoxy Frame based CNC MILL|
I test fitted and aligned the X axis saddle that carries the Z Axis today. Those following this post will remember I set the gantry yesterday using a 0.01mm dial indicator set against two bearing blocks. With the carriage in place I was able to use a straight edge allowing me to test the full travel of the carriage. there was a 0.005mm error in the height. No problem, I tweaked the height of the gantry casting to reduce this to less than 0.001mm along the full travel. Remarkably this was better than the accuracy I obtained setting up each rail individually, that was using 1 bearing block. The saddle is mounted on 4 bearings. Averaging must have worked in my favor. I am very pleased with the result.
Testing the X Axis travel height.
This photo shows testing the X axis travel near the tool in the horizontal plane.
Once the table is made It will be installed and tested in a similar manner.
Now that the rails are attached I have reassembled the cross member and test aligned it. This is not going to be the final assembly, there is further steps to go that will require it being disassembled again.
As the photos below show I have test aligned the components using the linear bearing sliders reference points. I wanted to test the alignment system built into the machine. As noted earlier in this post there are built in adjustment screws to enable the cross member to be set parallel and perpendicular to the to the rails that will support the table. I had no trouble aligning the reference points to .01mm on the dial indicator if it was the final assembly I would have used a .001mm indicator. The rails are already aligned to +-.001mm to my straight edge.
As you can see I have used a Moore & Wright precision square sitting on a parallel bridging two linear guide bearings.
The height adjustment is made using the two vertical jack screws on the top of the cross member, you can see a T handle and hex key if you study the photo. There are also 4 jack screws to set the gantry to perpendicularity to the table guide rails. see the two Allen keys I left in position. I have also marked the various points referred to with arrows.
Reflecting on the design of this machine and in particular the way the rails for X,Y,and Z are all located on flat planes that are generated separately and the way the rails were easily aligned to very high accuracy makes me realize that the the biggest errors will be caused by my scraping and lapping of the bearing support plates. Before assembling the machine I will revisit the lapping and try to improve the accuracy I documented earlier in the post. I guess this is being obsessive but It will be worth the effort. Unfortunately all the geometric errors, temperature effects, deflections due to gravity and vibration etc will be compounded, Time will tell what the final result will be?
Edited By John McNamara on 07/08/2019 14:32:01
Before reinstalling the cross member the ball screw mounting plates need to be set up. These plates are located in pockets in the casting attached by 4 M4 countersink screws. There is a space under the plate to allow its height to be adjusted to the correct mounting height for the ball screw assembly. once the final height is established the void behind the plate will be filled with epoxy by injecting it through the central hole in each plate.
The plates will be drilled for the ball screw bearing after marking out in position.
Three photos below:
Below is a photo of the tapping setup used to attach the rails. After drilling I used a modified T handle tap mounted in the drill press. The T handle has an attached shaft that slides in a bush mounted in the drill chuck. This keeps the tap vertical and also reduces the chance of tap breakage. After about fifty tapped holes in "gummy" 16mm steel laser plate I am pleased to say there was no breakage. Carefully cleaning the tap for each hole and liberal dose of Trefolex aided the process.
Type 25 linear rails as used here are drilled 7mm and counter-bored for for M6 cap screws. The difference between the 7mm hole and the 6mm screw allows the rail to be accurately positioned after drilling and tapping. This sounds like a lot however it relies on very accurate placement of the mounting holes. both with regard to spacing in this case 60mm, not just for one rail but two! Both rails must be parallel.
I thought on this for some time an the method I have designed is the result. It has worked very well. It relies on accurately positioning the rails before drilling using the cams on each side of the rail and a known accuracy ground straight edge. A stretched piano wire and a cheap USB microscope would also provide an excellent reference, particularly over several metres where straight edges become very heavy hard to find and expensive. I have done this before, it takes more work but the result will be the same.
The first step in the process is to accurately position the straight edge parallel to the rail supports, The cams have limited travel and an error here will create problems later. It does not have to be in the center as long as you have access to it for a dial indicator. I used a 0.001mm dial Indicator.
Once the straight edge was clamped in position (It must not be moved until the job is complete), the rails then can be positioned with the cams using the straight edge and dial indicator mounted on a linear bearing to align the rails to straight edge. The cams are drilled and countersunk for a 30mm M8 screw, by rotating the cams clockwise until they bind then then tightening this screw the cams press against the side of the rail foot. Once all the cams are tightened you will find the rail is clamped quite tightly. There is a bit of a learning process to get this procedure right but after a few trials I was able to reduce the error on the indicator to + - one 0.001mm division, as the rails are at this point not screwed down the error will be greater than this but good enough for drilling and tapping.
I used a G clamp to hold down each end of the rails, They were bowed down slightly. Don't assume that the brand new rails you receive from the factory (In this case Bosch Rexroth) will be straight. They have to be bolted down to a flat surface.
Below are 4 photos of the setup used to drill and position the rails using a straight edge.
I will describe attaching the saddle in more detail later, here it is temporarily bolted to the cross-member rail bearings. using the straight edge still installed below it runs within 0.001mm following the rails as expected.
I temporarily bolted on the Z axis carriage. centering the bearing rails to 165mm exactly.
The Z axis spindle; This is a big question?
Next is reinstall the cross member
|Thread: Coping with form and function|
If you have not seen Uri Tuchman's work before enjoy.
|Thread: Laser cut plates|
|Thread: DIY Epoxy Frame based CNC MILL|
And to the patient souls that want me to get cracking on this project. I have been away from the workshop, very frustrating....
The table is probably the most difficult of all the components of the machine to produce as a fabrication rather than a conventional cast iron casting. I did consider using a single thick steel plate, that would also work fine. as would a cast iron casting. With t-slots. or tapped holes, it will depend on what machinery is available to the builder.
The images below show the design I am using.
A better choice of aggregate would have made the process a little easier, The mix was hard to tamp down, As I explained casting over a thick granite surface plate made vibration of the whole mold impossible It would require a massive vibration table, And even if I could have vibrated it I would not like my surface plate to be subjected to that sort of abuse. So I simply tamped and tamped! I still got some surface defects I just filled them after the castings were de-molded. For the next build I Will used a finer aggregate that flows better.
I chose Megapoxy because It is well priced, It is fairly thin when mixed and and it does not contain solvents, I works well for me and the company that sells it is very helpful. I know West system's products are popular with the boat building fraternity in particular. I am sure it would work well also. I have used Araldite (The retail 24 hour product) To Make a cast in place bearing. Google "Epoxy bearing material and method", It also worked well in that application, It is a lot thicker than Megapoxy. And much more expensive. Fine for small quantity use.
I guess if you work with composites all the time you would make a high quality mold apply release agent and then cast it. My choice was to apply self adhesive film to all the laser steel panels before they were assembled is a departure from standard practice. No allowance for draft was made. Angling the sides of a mold as you would do for say a boat to allow easy release from the mold was needed as the panels were all removed one by one. I wanted 90 degree corners. The plastic sheet did its job well. Yes, I ground off all the sharp corners with a small angle grinder and a flap wheel, then fine coated with polyester body filler, sanded and applied paint. I got a good finish For a "one off" a lot quicker process than preparing a perfect multi part mold. Remember no draft.
Previously I tried using several coats of release wax. It was an melamine MDF mold. The wax got scratched by the aggregate while tamping. The mold had to be pried off in pieces. What waste of time.
I am starting to feel guilty for not posting here for a while....am held up at the moment waiting on the linear bearings and ball screws to arrive so I can get cracking.
|Thread: A close shave or why safety glasses are a must|
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