Member postings for John McNamara

Yes got the bug when I was in my 20's and started lessons on a PA28 piper. did about 20 hours. My instructor was David Colquhoun sadly passed, I will always remember him. he retired from the RAAF as Air Commodore DFC AFC, when he retired he kept flying and teaching at the royal aero club Moorabbin. As a young man I was in awe, Oh and what stories he could tell over a drink at the club bar, (at the end of the day)

Once David suggested I go along with him and pick up his Wife from Tullamarine Melbourne's main airport. So a flight plan was lodged and we got clearance not normally given! It helps to have high rank. It was a lot of work for him, he was in command, I was just an onlooker, entering controlled air space with the big planes flying so much faster than us was quite a job, we got our slot and landed. The tower gave us a gate, it was surreal to be in a single engine plane and pull up to a gate that a full size aircraft would normally use. we had to go through a little door and up the stairs on the side of the ramp. So we met up with his wife hopped back on the plane and off we went. What a day!

My partner was not keen on flying it worried her as we had started a family, money was tight too, so that was that. Another memorable flying day was when I went up in a Blanik 2 seater Glider at Benalla, country Victoria. This was an experience I will never forget, It was amazing.

Regards
John

Edited By John McNamara on 19/01/2019 14:40:32

Hi Mark

Greetings from Melbourne OZ

A Hercus Model A was the lathe I had on the top of my wish list when I was a young man. I still have the brochure! Never did get one due to lack of funds good luck to you with your find, Hercus machines were very well built in South Australia. you will find a real gem under all that dust.

Regards
John

Not much charity there Mick, authors have to eat too.

I just draw the line the correct length and rotate it. by entering degrees plus or minus.
Just follow the prompts on the command line.

Regards
John

Hi Jason

I issue quite a lot of building not engineering plans in A2 size for tendering.

I normally post them in the cloud at mediafire and issue a link for tenderers to download from.
I use black and white and shaded greyscale in preference to colour because the contractors get them printed in black and white even if they contain colour, Its cheaper!

And yes it makes little sense when you consider the value of the work they are quoting on.

Regards
John

Hi All

While thinking and browsing on Google looking for a spindle for my mill project I stumbled on this video on building a small spindle. as shown it uses 3C collets but that can be changed. The spindle is fitted with 3 bearings two at the front and a floating rear. Proper seals are fitted front and rear.

For fusion 360 users there is a free set of 3D plans for the spindle and the novel table top CNC lathe it is fitted to.

Link to video:
**LINK**

Link to plans:
**LINK**

Regards
John

Good point Jason re specifying the units used. I use Metric one drawing unit to 1mm no scaling.

Most laser cutters have a "set up" charge This can make a single part more expensive. It can be cheaper to order a thicker than you need part so that it is part of a bigger group.

Laser cutters are pretty busy businesses, If you provide good files you will be charged as a professional. Just email your requirements and the file set in a Zip file and most will reply with a quote in a day or two. (A separate zip file should be used for each material type and thickness. this avoids confusion)

Regards
John

Hi Duncan

Most laser cutters will have a specification for the file type and format they prefer.

All a laser cutter wants is a flat. No 3D file. on one layer without text. (some laser cutters will burn text into the parts for identification, ask if you want that done.)

The main thing is that all outlines on you drawing are perfectly closed at the ends without gaps or little tails..

Release 12 was an early version of Autocad. Nearly all software can read it so try that. A DXF file is a human readable, with difficulty, text file.

Regards
John

Edited By John McNamara on 14/01/2019 00:01:28

Hi all

And then there were two....

The columns that support the gantry cross member are now prepared and undercoated.

I increased the amount of epoxy to 18% by volume on the first and last layer (I placed and tamped the epoxy/aggregate in 5 layers) This gave a better finish.

The epoxy was allowed to cure then the side was covered in automotive body filler while still in the mold. This was allowed to cure then sanded flat using the mold as an edge guide. The other sides were also prepared after removing the casting after a 24 hour cure. As you can see from the painted images below the result is very crisp lines. I used a vibrating half sheet power sander and a half sheet plasterers joint sander by hand. All the non steel edges were rounded carefully by hand to about a 1.5mm radius. Finishing as usual took a fair amount of time, Finally a coat of etch primer was applied, There are still a few blemishes they will be fixed before the top coat which will be done after the final assembly of the frame is completed.

Comparing the two columns visually the steel mating surfaces are in perfect alignment. I will measure the actual error later when the next mold is removed from the surface plate. The design allows for a maximum misalignment of 2mm. I am guessing the error is under 0.25mm. The column on the left has masking tape over the metal face.

Next is the base, when this is poured I will be able to test assemble the machine and check for alignment, there should not be any problems so far all the parts are within spec. The columns are going to be screwed straight down on the base without any adjustment, hence the importance of their accuracy. When the gantry cross member is placed on the step and bolted in position and the built in jacks used to align the linear bearings it carries to the base ways there will be a small gap left that will be filled with epoxy before final assembly.

The following paper is worth reading. it covers building a precision machine, it uses the same method to assemble the components.

**LINK**

Regards
John

The link to a Google search worked fine here, anyway try these:

One UK one state side.

**LINK**

**LINK**

I had read of this problem with Sony before.

Yes Youtube puts an adv in front of many videos, not a bug just a pain in the a...s

Regards
John

Edited By John McNamara on 11/01/2019 07:29:41

Hi Clive

Do you have a generic charger? some users have posted videos and have found it will charge a battery that Mr Sony rejects. It outsmarts the smart (SIC) chip.

**LINK**

Regards
John

Hi Chris

I don't use Alibre but i think drawing a right angle pipe can be done with the sweep command. I use Autocad which also has a sweep command. so I checked on google and found this:

**LINK**

Regards
John

Hi Ian

Yes he is a good presenter, his video posts on engineering history are very well thought out.

**LINK**

Regards
John

Hi All

Finding and editing images, with and without copyright, I found this video very informative.

Towards the end it deals with some free tools to edit photo images. in a word cool!

1**LINK**

Regards
John

Edited By John McNamara on 07/01/2019 03:27:26

Hi Marcus

I allowed for double nut Asian rolled ball screws this should reduce the backlash somewhat while not breaking the budget. There will be more lead error than from precision ground ball screws. The same applies to the linear rails. however if higher spec rails are needed they should just bolt straight in as long as the hole spacing is 60mm and the overall height from the bottom of rail to to top of the slider block. Many manufacturers offer this as standard.

**LINK**

For the timing belts GT2 belts appear to offer the best accuracy, more expensive than AT style belts.

Edited By John McNamara on 06/01/2019 12:56:48

Thanks Fellas

Yes clear resin mold would be a great conversation piece.

I would be tempted to experiment with polymer concrete if the shrinkage and cracking can be controlled instead of epoxy but that will be after the Epoxy/aggregate mill is built.

Its pretty clear that the total accuracy of the machine will be a lot less than the accuracy I was able to apparently achieve with the steel rail mounts, I said apparently because do not really know if the surface plate is truly flat to inspection grade i suspect it is within about 3 tenths or for that matter if the indicators I used are in perfect order although I think they are.

Alexander J Slocomb at MIT mentions an "error budget" in his book "precision machine design". also in this paper,

"Understanding and modeling errors in machines"
W >**LINK**orth reading, it confirms common sense that overall the accuracy of a machine will be the sum of all the separate error generating parts. We must assume that each part will generate some error, nothing is perfect.

The mil I am building is not going to be a micron level super machine, hopefully it will be a lot stiffer and accurate than many of the small import mills being offered and it is designed for CNC at a budget. I wanted the design to be simple enough to allow a skilled person with a small lathe, a drill press, access to surface plate, hand and measuring tools and access to laser cutting for the mold and some of the machine parts. Optionally the mold could be made from MDF by hand.

So far the machine has rewarded me greatly, every day it explains very clearly what works and what can be improved. I the end it will reflect the sum of the parts.

What will I make with it? more machines!

Hi All

The first Gantry column has been cast and preparation for undercoating started.
The other column is next. The same mold will be used, By turning the base plate upside down and rotating all the mold side plates 180 deg you get a mirror image of the first mold. A bit like making a pair of shoes. The left column does not have to provide for a motor so those parts will not be used.

The steel molds are amazing, every part just fits together, there is no draft. I did not use any mold release. The self adhesive plastic sheeting works really well, a light tap and the mold parts just fall apart. there is a bit of mess I did not protect every face. A quick clean on a wire wheel and the mess is gone.

I have been working on the Epoxy / crushed granite mix mixing about 5 litres of material at a time then placing it in layers, Due to the complexity of the molds and the many inserted steel components they contain I think I will have to increase the percentage of epoxy above 15% to get a wetter more flowing mix. More experimentation is needed. Less epoxy is better (stiffer).The next cast will be the left column.

Mold prepared inserts all attached.

Mold filled with epoxy/granite, the top layer is 5mm of epoxy/sand for a smoother finish.

Body filler applied and sanded in preparation for painting

Motor pocket metal form work partially removed. See removable cast in position motor plate at bottom of pocket.The form work was wrapped in duct tape prior to casting this provides clearance making it easy to remove.The M8 threaded rods attach the mold base and locate the motor plate and form work in exact position in the mold.

Removable motor plate cast in position. It is wrapped in adhesive plastic film, this provides clearance for removal and epoxy won't stick to it.

View showing the cast in position mild steel 10mm mild steel shoe and 2.5mm mounting faces for the gantry attached to the column

i will have to try making up a spring tool one day

A doodle in Google found a few!

**LINK**

My first lathe an old flat belt Colchester that came from a picture theatre. It was installed in the basement for the ushers to use during WW2, morale was important during wartime so theater's were kept open. When the film was running the Ushers spent their time making parts. This particular lathe was just forgotten down in that basement for a quarter of a century. That is until I heard about it. It was my first lathe, I was in heaven! When I got it home it still had a jig on the face plate for profiling brushes used in submarines I was told by the owner.

The confusion between the US and the metric world in relation to what measure a Micron describes is confusing.

Being part of the metric world I have to teach myself to use the full metric "Micrometre" not the abbreviation Micron on documentation to make it clear what measurement system is being used.

Some parts of the US think a Micron is is a ten thousandth of an inch.

A Micrometre is actually about 0.4 approx of a ten thousandth of an inch. Less than half as big

Or 0.0000394"