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Member postings for John McNamara

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: DIY Epoxy Frame based CNC MILL
29/06/2019 02:35:15

Hi Chris

And to the patient souls that want me to get cracking on this project. I have been away from the workshop, very frustrating....

The base design is uses laser cut 10mm plates spaced by shouldered steel inserts that are threaded and will form the points of attachment for work pieces. there are also inserts threaded to attach the bearing blocks. Rather than have the epoxy visible on the sides I designed side plates that also locate all thread reinforcement bars. the completed assembly is filled with epoxy from the underside. through a multiplicity of holes.

Once assembled and mineral cast the top and bottom will need to be made flat and parallel. this is a job i plan to farm out to a surface grinding contractor, I could do it by hand scraping around all those holes! but it would take a lot of time, it is also above my skill level. I could also mill it on my vertical mill, but not to the level of accuracy obtained by grinding.

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.
The 25 x 25mm Aluminium angles are part of the swarf guarding

13/05/2019 16:47:19

Hi Craig

That's a difficult question for me being a bit of a perfectionist. There are many small details that I could improve on and that can go on infinitum! However There is nothing that I really regard as a gotcha,

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.

Maybe my biggest error is in not starting my project sooner! Too much research and overthinking and not enough building. The Heavily steel reinforced machine frame I have made has surprised me. Its turned out far better than I imagined.

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.

Regards
John

Thread: A close shave or why safety glasses are a must
06/05/2019 16:20:00

Hi

Maybe a bullet proof vest would help? But then again maybe not

**LINK**

Regards
John

Thread: Autocad 2000 Cant draw at a chosen angle.
29/04/2019 02:23:59

Hi

Better Autocad drawing technique.

Snap (F9) I almost never use. I also leave Grid (F7) off, the little points are annoying. With ortho (F8) on select a point, enter L for line then drag the mouse in the direction you want to go in and enter a specific length, followed by enter. once the first line is drawn you can keep adding lines by entering a new length and pressing enter. Practice doing this say drawing a box. At any time entering C will close the set of lines you have just drawn so drawing a box only takes 3 lines plus C to make the last line.

I do keep Osnap on (F3) most of the time. If you enter Osnap in the command line you can set the points it will snap to.

Oh Important, I Always start my first line at XYZ zero. Enter L then 0,0,0 as numerals not 0's then [enter] then mouse the direction then enter a length then [Enter]. This way the first part of an object (Normally the bottom left hand corner is set at true XYZ zero). Ortho (F8) should be on. Yeah it could be an angled line, I like to start with a straight line.

Drawing lines of a specific length will become second nature after a while. Using snap gets in the way as it limits you to a standard grid spacing. Most real life objects are not built that way.

Regards
John

Thread: Impressive Workshop in Germany
15/04/2019 01:24:02

Hi all and especially the doubters.

The link below is to his instagram like blog, it details the workshop tool restorations done and many other inovations.
The machines did not look the way they do now.

Oh! and a warning one of the photos shows him wearing shoes, and beware there is also a broom shown!

If you double click on the images they open up often leading to a set of other images.

I do like the way he has approached a 3D printer design, Not the cobbled up bits of plastic that you see all over the net. I don't have a 3D printer but I am tempted to have a crack along similar lines after the Epoxy Mill project is finished, I am waiting for the bearings and ball screws.

Link: On my machine It loaded slowly over a minute or so the images are high res.
**LINK**

Regards
John

 

Edited By John McNamara on 15/04/2019 01:37:58

Thread: Vickers Bl 8 inch Howitzer cannon of 1917
14/04/2019 13:43:33

I am in awe Mal
Photographic realism in 3D
Looking forward to your next post

Thread: Impressive Workshop in Germany
14/04/2019 13:30:53

Very impressive,

Check out the 3D printer mechanism near the end of the video.

Thread: Please help machining
01/04/2019 23:19:05

Hi

You may find a sewing machine needle that can be adapted to your machine, maybe you could get a longer needle and remove the thread eye and make a blunt point most will already have a groove. The material will be high quality hardened steel so the result will be durable. It can be ground easily but not turned.

Locally industrial sewing machine suppliers will have needles.

The link below may assist also, Schmetz are a leading manufacturer of needles.
Send them the dimensions of your needle
**LINK**

Regards
John

Thread: DIY Epoxy Frame based CNC MILL
23/03/2019 23:09:27

Hi Douglas
Thanks Vic

It is not the end of the world if you miss an insert, or have to add one later. Epoxy/aggregate behaves the same way as normal concrete, you can drill it with a masonry drill. A new steel insert can then be made and epoxied in place, this is done millions of times a day on building sites.

More difficult is machining epoxy/aggregate. It can be done with carbide tools but they will be blunted very quickly. The saddle photos show a lot of large holes as you can see they have been filled to the brim with material. For the saddle I only used washed sand as the aggregate, if I had used gravel it would not have been able to flow into the small spaces in the mold. epoxy sand alone is not that difficult to rough machine, Automotive body filler machines quite well. BTW body filler shrinks a lot on curing.

I used some automotive body filler to smooth the surface of the holes before machining them. The machining went well enough, I did a couple of roughing cuts then finish machined the surface with a .004" cut. Yes It did cost me 2 points on the triangular tool insert. The 25mm holder has provision for two tips however I have found for this operation one tip gives a better finish, I ran at 1220rpm 9 inches a minute feed, about .007" feed per rev. A bit on the fast side for me however I found slower spindle speeds produced a rougher finish. The mild steel material is a bit gummy.

Regards
John

Edited By John McNamara on 23/03/2019 23:16:38

23/03/2019 11:06:18

Hi All
15 Images follow

It’s been a while since I posted on the epoxy mill, Inspired by the accuracy of the castings made so far I decided not to use the low cost option Asian bearings and ball screws. Instead I will use Hiwin Taiwanese bearings these can be ordered to a proper engineering specification. I have asked suppliers to quote. This has imposed a delay. While waiting for the Hiwin bearings I have used some Bosch Rexroth bearings I have in stock for testing, these are earmarked for a CNC Router to be built in the future. They have exactly the same dimensions as the Hiwin bearings, so are interchangeable as long as you don’t mix manufacturers, the rail profiles are different. I have used them in the photos below. The router requires 2400 travel and I have two 3 metre lengths and some short lengths acquired as new second hand, hence the need to keep the stock bearings together as a set for use later. It would have been nice to use Bosch Rexroth Linear rails for the CNC Mill however they cost more than double the cost of Hiwin. While waiting for the linear rails and ball screws there is plenty to do.

My original plan was to only use the surface plate for flattening surfaces, I did this for the X and Y rail mounts as described earlier in his post it worked well however it was very slow progress. For the saddle I have used my vertical mill. It is a Shizouka VHRG, being a rather old machine the knee is a little worn. In order to get the best accuracy I had to use the overarm travel as the cross feed leaving the knee locked. The over arm never gets much use over the life of a machine so there is no wear at all. I also set some bolts in the tee slots and machined them using the overarm method. By doing this the only the table longitudinal travel and the over arm travel influences the cut. I am very pleased with the results.

The Z axis saddle casting has been done, This unit is a little different to the frame castings already made, it is more of a hybrid being made from 10mm laser cut steel plates and quite a number of drilled and tapped spacers that have a good fitting shoulders inserted into laser cut holes and glued in with epoxy making a very rigid unit. The spacers were very turned carefully to shoulder length.
This saddle unit fits into a laser cut steel mold that forms the side and the centre channel walls, it also locates several threaded inserts on the top of the unit. It will be cast this week

The saddle unit caries the Z axis, when thinking on the Z axis design I anguished for some time on the best way to set up the linear rails, should the linear bearings move or the rails move? Or to put it another way should I attach the linear bearings to the z axis and put the rails on the saddle or the other way around with the rails on the moving Z axis and the linear bearings on the saddle?
In the end I chose to attach the rails to the Z axis and put the linear bearings in the saddle.

With the saddle and the Z cast and machined at last they can be test fitted for the first time. It is exciting to see the actual components sitting on the bench having seen them on the computer screen for so long, now they have come to life.

Saddle / Z axis assembly

Inserts inserted

Ready for casting

Placed in Mold

Milling Face

Face milled

Bearing blocks test fit OK

Limit Switch housing

Z axis retracted

Z axis extended

limit switch housings fitted

Z axis drive motor plate attached

Set up for milling Milling bolt heads flat for perfect alignment with travel.

Edited By John McNamara on 23/03/2019 11:3

Thread: Cap head screws
22/03/2019 06:30:39

The problem with boxes to store parts is space, and fastenings come in many lengths and head types. The boxes will will be half full or less.
For me the answer is small zip lock bags, they will keep the parts separate, you can mark up a paper tag that can be placed in the bag. some have a writing surface on the outside, they are flexible allowing them to nestle, I keep these in larger part boxes sorted by say the thread diameter. A lot less wasted space.

Zip lock bags are also very inexpensive and they keep moisture out, less rust....

Regards
John

21/03/2019 11:13:13

I avoid buying fastenings from the local hardware shop, the little blister packs tend to contain rather low quality no name stuff. they are also rather expensive. The better way is to purchase fastenings from an industrial supplier. small fastenings come in various box quantity lots starting at 100. Often a whole box will cost significantly less than a few fasteners in blister packs. If you google Industrial fastenings for your town or city you may be surprised how many there are.
Ring one or two and check stock for a fastening you are looking for. (Many suppliers will supply small lots as well)

This UK company popped up in a google search I do not know them at all however the website is easy to use as a reference point.
**LINK**

I am sure the members of the forum will have other options.

Regards
John

Edited By John McNamara on 21/03/2019 11:16:02

Thread: Recommended base flashing for an external wall
21/03/2019 08:00:34

A couple of rows of brick set in a high strength mortar will keep your steel sheeting out of the dirt. Then use a formed metal flashing the slips up behind the sheeting across the brickwork then down over the outside brick edge say 40mm it will keep the water out. Lead will also work however it may cost more than the formed sheet and it can look a little rough. You will l also need to apply a waterproof membrane inside against the concrete floor and brick corner (Use masking tape to keep the edge on the floor neat). If you are painting the outside I would also apply membrane to the bricks and the edge of the slab before painting.

Steel will rust quite quickly if it is covered by soil.

Regards
John

Thread: Precision division plates
10/03/2019 03:49:44

Hi All

An online calculator to generate a a Hirth coupling. I remember seeing this link a while back a bit of searching and I found it, It is still there! quite well executed too.

Hirth coupling Calculator.

Regards
John

Edited By John McNamara on 10/03/2019 03:50:11

Thread: How do you make a lifting eye
07/03/2019 14:35:00

Hi

Maybe a cable eye bolt can be cut down?


**LINK**

Thread: Mechanisms in modern engineering design Artobolevsky
07/03/2019 14:14:27

Just noticed these.

5 volumes in 6 parts. Maybe a 7th coming

A little slow to download, well worth the wait.
From Mir Publishers USSR. Mid 20th century.

Are books like these even published these days?

**LINK**

Regards
John

Edited By John McNamara on 07/03/2019 14:17:27

Thread: fundamentals of machine design, orlov
07/03/2019 08:09:43

Hi All

A while back I found this set of books in a bookshop. There are actually 5 but the first three are the most important.

I really value them.

Orlov explains by example showing good and bad designs.

**LINK**

Regards
John

Thread: Precision division plates
07/03/2019 07:19:28

Hi Mike Poole

When I think of high accuracy in the 20th century I think of Moore Tool
**LINK**

This company designed one of the highest accuracy mechanical rotary tables ever made. It uses a hirth coupling to form the 1440 divisions it divided a circle into than a further vernier for the spaces between the divisions.

I had not seen the ball method of dividing that looks rather interesting! If the balls were set in two precision grooved plates and epoxied in place, they would have to be absolutely level in one plane, you would have the two sides of a hirth type coupling.

A coupling of this type when used for indexing will tend to average out any errors. Moore recognised this and used it for their highest accuracy tables. It is described in depth in the Book Foundations of mechanical accuracy. One of the great mechanical engineering reads.
**LINK**

Hirth Coupling.
**LINK**

Gee I love first principles in engineering.

Regards
John

Edited By John McNamara on 07/03/2019 07:20:15

Thread: AutoCAD substitute
04/03/2019 21:50:02

Hi Glyn

I purchased Autocad a long time ago and have kept it updated up to now. At least I own it as it was sold to me under their old licence where you bought the program. Now you can only buy a subscription. They keep asking me to switch. Not a chance there. When I retire and stop updating it I can keep using it. These days they only do cosmetic changes anyway.

Anyway I did a bit of searching and found the following links.

For 3D modeling machinery Fusion360 is worth looking into, I downloaded it (Free to hobby users) The interface is not at all like Autocad, However the built in CAM is very enticing. Compared to Autocad it is in my view totally unsuitable for designing buildings beyond say a dog kennel.

**LINK**

**LINK**

**LINK**

**LINK**

Regards
John

Thread: DIY Epoxy Frame based CNC MILL
01/03/2019 14:50:54

Hi Ian

I do not have a vibrating table although I have seen a few you tube videos of one being used. The molds were placed on the granite surface plate to align the bearing mounts in the case of the base and main cross member I did not want those to be vibrated. Note there are holes in the mold, the bearing mounts sit directly on the granite only separated by a thin film to protect the granite from any epoxy leakage that would glue the whole setup together and damage the surface plate.

The granite aggregate came from a Victorian quarry. on the Mornington peninsula. The type of rock a quarry mines is location specific I just made a couple of phone calls and I found one that mined granite.
I have also used coarse silica sand and fine mixed gravel from a garden supply with epoxy It worked OK,

Here is a Google search that should give a good idea of the process and many PDF documents. Note how by searching for images it shows if a document will open, I find this useful.
**LINK**

I am using DC servo motors with integral 1000 count encoders. All the motors are located on laser cut steel plates to make it easy to swap I left plenty of room for the motors.

Regards
John

Edited By John McNamara on 01/03/2019 14:52:20

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