Member postings for John McNamara

I am guessing that the force needed to clamp the work is more than the force that would cause injury to a person.

When an individual builds a machine alone for personal use that person has to accept all responsibility for the safety of the mechanism.

Apart from pointing out the possible risks. I would be hesitant offering advice to another person on how such a device may be constructed unless it was made safe by the installation of guards that stopped all access while the device is switched on or working.

Safety systems have to be robust. Electronic means of protection have to have built in redundancy, they have to be duplicated, better still they should be backed up by a physical guard barrier.

This paper is a useful guide.
**LINK**

Regards
John

Edited By John McNamara on 03/01/2019 02:01:45

Edited By John McNamara on 03/01/2019 02:02:55

Given the small size if you don't have access to a lathe.

Get some grade 8 washers. place them on a bolt with a nut to clamp them then chuck them in an electric drill and then carefully file the chamfer.
polished up with fine wet and dry paper both in the drill and on the face they should look fine.

Regards
John

Hi All

John Haine has used a simple contact limit switch method used by many DIY CNC router builders to sense the tool height by placing an insulated contact plate on the bed and lowering the tool until it contacts the plate that works well. If the contact can be kept clear of contamination it will work accurately.

Robert Atkinson mentioned that break contacts are more reliable. I agree and a while back made a small experiment to do research on wire alignment using direct contact (on break of contact). Wire alignment is still used to align large machines. Google Cern wire alignment.

**LINK**

Three images below:

Accuracy, repeatability and low cost were the main objectives. It also had to be able to apply a force sufficient move a small machine slide not just for contact testing.

The device comprises two 25mm sq BMS levers pivoting on short spring steel flexures, a flexure also drives the plunger located in the reamed round tube. the lever ratio is 10:1 The drive is a A 400 count per rev half stepped step motor driving a 1.25mm screw via a timing 4:1 ratio timing belt. Note the substantial spring that forces the levers apart and the way the motor mount is attached to the semicircular pivot. this maintains correct alignment as the levers move. yes the timing belt is too long but it was in my stock!

The levers provide 10:1 primary reduction closest to the measuring point, with negligible backlash. I used this mechanical system hand driven, no step motor or timing belt on a grinder head allowing very accurate wheel positioning to 0.0001” and it was repeatable.

The control system (Created by my mate Leo) is a baby Arduino, a stepper driver and a small touch panel. Many thanks due. The parts were remarkably inexpensive.

A number of tests were done; the test shown was a piece of stretched high tensile carbon steel piano wire that contacted a stainless steel pin. Not ideal, gold would no doubt be better but I wanted to see what simpler materials could do. The wire and contact pin was wiped clean. Apologies for the rough setup but it did the job and worked.

The control system was programmed to move the pin slowly into the stretched wire at various speeds then back off until contact was lost. The process was repeated thousands of times.

Overall it behaved as planned, the dial indicator needle constantly moving to the same position at each measurement. around 3 tenth's accuracy with a few outliers caused by mechanical sticking I plan to use this system in the future, a few improvements are planned .

Regards
John

Hi All

The workshop has been a little quiet over Christmas, cant wait to get back to working on the project.

I posted a note on limit switches here: **LINK**

I think I will stick to the plan at this stage however the ability to home the machine to within a few microns is a possible upgrade.

Regards
John

Edited By John McNamara on 31/12/2018 01:16:30

Hi John

I provided housings for standard size plunger type industrial micro switches for the Epoxy V mill I am building. these switched are very robust and can be purchased for under 20 dollars from a known manufacturer.or a lot less from unknown Asian makers. I used these switches on another CNC project a router they continue to work well in spite of the wood dust. repeatability is around 0.003"

The housing is tab and slot construction 2.5mm laser cut steel (not shown is the m3 screws that hold it together although the tabs do most of the work. they are very rigid.

This article is worth a read

In particular the section on precision micro switches with Micron level repeatability.

**LINK**

I did a google search.

**LINK**

I quickly found these as an example, but did not do an extensive review of what is on offer.
For around 40 - 50 dollars pretty good accuracy 5 - 10 micron 120 dollars 0.5 micron

I will stick the the mechanical switches for my project however if retro fitting a lathe where a single home switch is needed I would be tempted.

**LINK**

Regards
John

PS Link to my project **LINK**

Hi all.

A very Merry Christmas from OZ.

Looking forward to 2019, lots of projects.

Regards
John, Kim, Peter and moggy Bella.

For cheap hydraulic power, the kits sold for panel beaters are worth a look.
You can make more tooling to work with them.

**LINK**

Sharp HSS tool side cutting tool plenty of rake, light feed. Dead on centre height. Cut in one pass from maybe 10 - 12mm bar. this should self support itself depending on the length you require.

Effectively you are leaving a 1/16 thick long pip!

Oh and allow for a few tests to get it right.

Hi

From the video It appears that the "bearing play" is the bearing cage moving, the actual rollers appear to be stationary.

To measure the radial run out I regard any non mating outside surface on the spindle as suspect, only the spindle inside and outside tapers and the chuck mounting face (if they are in good order and have not been worked on) can give a reasonable indication.

If it appears that the mating faces have been worked on I would set a known precision ground bar say 400mm long by at least 40mm diameter in the 4 jaw chuck and after setting it dead true I would check that for run out near the chuck; if it can be set dead true it would make me wonder maybe the bearings are OK, at least without a load? The final test would be to apply a load to the end of the bar to see if there is play in the bearings under load. by using a known roundness bar you have eliminated errors caused by worn surfaces on the spindle nose.

Once the above test has been set up you can place a insert a reasonably well fitted bar in the back end of the spindle and apply radial pressure while checking for errors at the chuck end, you may need a helper.

Hope this helps, it should give a better indication of current condition..

Hi RMA

I have a Daimler Super V8 1999 year 130km , It runs very well. I am the second owner, mechanically it has been fine, no rust. It is a thirsty car. Nice for weekend outings. Mine does not show any underbody rust. Salt is not used on all but a few alpine roads in Australia. I know the original owner and that it has always been garaged.

The bigger issue for the V8 is the plastic! timing chain tensioners they can crack and fail causing severe engine damage. have they been done on yours? the revised units are metal.

I guess you know about the Jag forum link below using google to search XJ8 posts.

**LINK**

Regards
John

Edited By John McNamara on 16/12/2018 22:34:38

Hi Larry and Marcus

Thanks for the words of support. Glad to see the threaded rod is low cost for you too. I am not sure the galvanized type would stand up well in severe conditions it is very easy to remove the coating with a wire wheel. I suspect it is applied by a process other than hot dipping. for this project it does not matter, raw steel would have been fine, I just used what was in stock from the local Bunnings store All i want is "reo" with threaded ends for fittings.

Hi All

This weekend I continued the lapping of the rail mounts, its been slow going to get them down to about +- 0.0001" one division on the indicator is .0005" I Interpolated between the divisions, however this overstates the overall accuracy obtained. Temperature and measurement errors have an effect on the results as well. However I am very pleased with the results so far.

I ground the 25 x 25mm mild steel bar face flat for this stage it was not perfect and was affecting the results.
As shown below I used various grades of paper from very rough 60 grit for ripping down 120 grit aluminium oxide finishing off with 40 micron Mylar backed strip. I found the Aluminium oxide paper to be better than emery. As you can see by the number of used strips the paper looses its sharpness and looses cutting power on the large lap fresh paper cuts fast, it will be fine for other work

I will stop the lapping process lapping here until the linear rails arrive. it will be interesting to see how accurate they are when attached and aligned by the cams. Any further adjustments will be made then.

It is time to start the two column castings.

Hi All I was asked these questions at another place.

In answer to your questions A and B.

A. “To get ground stock (can be bought ground, but suspect $$$), predrill (most) holes and cast against surface plate as you have done”

I considered precision ground stock and phoned around to locate a source, it was available at a cost, quite a lot actually; however the supplier would not guarantee flatness on longer lengths. They would provide a tolerance for constant thickness but not flatness, however for this project only one side has to be flat the other side is buried in the casting.

Laser cutting precision ground stock which is normally a water or oil hardening carbon steel is likely to make any hole or laser cut edge very hard. Also my laser cutter charges extra for precise positioning small pieces of material, they prefer to work with large plates. This hardening also occurs to a small extent with mild steel, making it hard going for high speed steel tools however I did not have a problem with HSS on the steel supplied by the laser cutter.

If I was able to locate precision ground stock with a guaranteed flatness it would have to be machined to size and the 16mm holes for the cam pins would have to be drilled. These holes do not have to be located to high accuracy so marking out and centre punching in the normal way would be fine. The cams will compensate for any small errors.

The 16mm thick standard mild steel plate supplied by the laser cutter has a reasonable surface finish free of the normal flaky scale you get on black bar stock, there is a black oxide coating and some mill marks. After cutting it is not flat there was heat distortion, bowing of the 16mm axis in particular. I mechanically straightened the pieces and then sent them to a firm with a surface grinder. This was not a success as they did not completely flatten then pieces. I suspect their operator was not up to the job. The big enemy is the magnetic chuck. Grinding long pieces requires packing the work so the chuck does not pull any bowing down before grinding a side then, then turning it over and repeating the process for the other side. This process may have to be repeated several times until any stresses are relieved and the piece will lay flat on the surface table. Even better would be to have the part stress relieved professionally another cost.

In the end I hand lapped the errors left by the surface grinder. As the post above shows there were some residual errors.
I have been working on them with the lap and now the maximum error is .001” over 800mm testing the part on the surface plate with an indicator. I am confident I can get that down to a tenth or so, however just turning the part 90 degrees would probably change that, gravity is a universal force. I guess I could set the part up on its airy point’s that would possibly reduce the measurement error however temperature is also a variable. My workshop has a skylight. We happened to have a hot day yesterday a high of 33 today the high was 20. As expected my error measurements changed with the sun shining on the part; the top face was heated and the face bowed up. Digging the depths of high accuracy is an interesting challenge.

Question B. “Use mild steel bar stock, cast in standard mold, not requiring surface plate, and pay someone with a big cnc mill to quickly machine the steel and drill the holes?”

That will work no problem, apart from finding a contractor that has a CNC machine and equipment that can handle large heavy parts and cost.

It was tempting me to take that option, were it not for the desire to to find out what is possible using a surface plate, small lathe and basic tools. The laser cut mould is optional it could be made of MDF for one time use. The machine does use laser cut parts, they could also be made by hand a large time cost. If I manage to make a workable machine and demonstrate a method that worked I hope others will maybe create their own designs and contribute improvements to the methods I have used for this machine.

Edited By John McNamara on 13/12/2018 14:32:21

I am speechless, that machine is one of the worst new imports I have ever seen.

Well almost speechless, however the invective I would use for the vendor is not in polite use.

Back it goes all expenses paid by the vendor.
And only a full cash refund including any bank feed paid by the purchaser.

regards
John

Hi all

I have cleaned up the casting, rounding edges and filling blemishes with body filler, there were more blemishes than I would have liked, the part has been given a quick undercoat, once the whole machine is complete it will be detailed and properly painted. The part is very massive too heavy for me to lift. Tapping it with a hammer yields a dull click, even on the metal parts. due to the damping properties of mineral cast epoxy.

The next step of this project is possibly the most important. the accuracy of the machine depends on this stage being a success. The accuracy depends on the rail mounting points being both straight to fine limits and co planar. As the XY and Z axis are completed they must also be correctly located in relationship to each other. At this point we are dealing with the X crossmember axis only.

As stated earlier in this forum thread a surface plate was used as used to align the steel rail supports. the surface plate partly formed the bottom of the mold. there were holes in the mold and the steel rail support bars projected trough these holes in direct contact with the surface plate.

To test the accuracy of the rail supports the part was placed on shop made jacks. They bear against a cast in steel face not seen, the columns will mate against that face.


The part was aligned to the surface plate to within .0001" using a dial indicator, one div = .0005", mounted on a very rigid Mercer base. Once set up measurements were repeatable to within .0001" or better. The one knob type indicator mag bases being sold widely are simply not up to it.

The rail support bars 70 x 16mm in cross section were ground and hand lap/ground on one side prior to casting, this was not a complete success, the bars were too flexible and I found it quite difficult to get repeatable markings from he bluing. as the results show below there was some error after casting. the upper rail in the picture with two rows of tape had a maximum error of .0008" bowing op in the middle the second row of tape shows the error reduced by lapping to .0004" not a huge job a bit over an hour so far, there was not a lot of metal to remove. More to do, I want it as close as I can get it within the limits of my tools.

The other rail has an error of .0018" almost two thou, mainly caused by a dip at one end
It will take a little longer to adjust.

Simple steel laps made from 25mm x 25mm mild steel. The abrasive is 40 micron mylar on the longer lap 120 grit aluminium oxide on the shorter lap for roughing. not glued on just held with fastenings at the ends. Every workshop should have these, mine never leave the bench

When lapping I sometimes make a small light scribe line to help me gauge progress between indicator checks that take time due to cleaning, not too heavy on the scriber ! see below.

The surface plate It must be kept perfectly clean and free of grinding particles, you cant just drag the indicator around.

The surface plate itself may not be perfect I purchased it from a toolmaker he said it was grade A. as a double check I am also checking the flatness with a precision straight edge, a recent find brand new still in the wax paper. note the date! Both edges give the same readings indicating it has not moved in 73 years.

I must admit I am excited by these results. It is clear that rethink of the rail mounting support design is in order, I would like to improve the preparation prior to molding. They will have to be stiffer and my lapping skills will have to get better.

On the other hand the existing method has worked very w

Hi All

The first casting was made today!

Image below
This is the last time I will see all the components I made. as you can see there are no complicated parts.
Mainly a lot of simple lathe work, tapping holes and preparing threaded rod.
A few laser cut 2.5mm sheet parts. deliberately rough ground on one side for adhesion.
Also 2 16mm x 70 rail supports. I lapped one side flat (A lot of work)

Before starting the cast all the parts have to be cleaned with solvent I used methylated spirits.

The surface plate was very carefully cleaned then checked with the palm of the (clean) hand, this will detect tiny specks that you cannot see.

The surface plate was then covered with a new sheet of 80 gsm plan paper (with 2 large slots cut out 25mm all around wider than the bearing support rails) The bearing supports rails sit on waxed baking paper not plan paper, (When I measured it I found it has very uniform thickness) This is to protect the granite surface plate. The waxed baking paper was sprayed around the edges with silicone.

The 5mm thick mold bottom plate was then placed on the surface plate.Note all the long nuts screwed in from the bottom of the plate in countersunk holes all carefully checked that no CSK bolt head sits proud of the bottom of the plate.

The top of the plate is covered with self adhesive plastic to stop the epoxy sticking.

Laser cut mold parts ready for assembly. These will be reused.

Poured!
I am sorry I don't have any pictures of the molding process I was kept very busy placing and tamping the 4 mixes of about 5 litres of Epoxy aggregate This was topped of by a thin layer of sand epoxy as seen above.
I will try to get a helper to do the photographs on the next pour, There are 4 pours to go!
As you can see the finish is so so, I kept the mix ratio to 14% epoxy by volume, this makes a fairly stiff mix.
The 8mm Aggregate contained a few larger stones, For the next pour I will sieve the larger stones out. they made the tamping more difficult. I did it layer by layer. so the layer on the bottom would have been unworkable (but still very sticky) by the time I was doing the top layer.
The process took about 1.5 hours The weather was cool so there was no problem with the mix going off before it was placed

Exotherm? The mixing bucket got slightly warm only. When placed in the mold I could not detect any heat with my hand.

The mix was one part aggregate and about and 0,45 parts washed fine sand.
This was determined by filling a container with aggregate then slowly pouring the sand over the aggregate until no more sand could be poured in. I used a mechanical vibration. Note when this process was finished the volume is only one part. The sand simply filled the voids between the aggregate particles.
The final step is to sieve the aggregate to recover the sand which was then measured to determine its volume.

I used a cheap disposable bucket to mix with an 2500 Watt electric drill, and I needed those watts it was only just enough. The agitator was a low cost spiral mixing unit purchased from the local hardware for about 10 dollars.
Power mixing is essential.

This is for Neil Wyatt. Yes the Limit switch wiring is routed through the casting, they will go straight into the control box shown earlier this forum thread.

it's been a long journey, at last it will be possible to test how accurately the bearing support rails are aligned. Hopefully they will not have moved during the cure and I will not have to re-lap them.
The next step is to strip the mold, I will wait 48 hours at least to allow the material to cure.
This will be followed by attending to any small voids with body filler grinding off any rough spots, and rounding sharp edges followed by epoxy paint.

Regards
John

Yes Martin I meant if you don't have a horizontal mill.

I am not sure why the setup should sing unless the clamp was too far away from the cut allowing the thin plate to vibrate.

It is hard to clamp thin plate down unless the clamp face is ground perfectly flat. I sometimes place a piece of suspension file cardboard under the clamp to keep the work pressed against the table (the older ones are harder and better for this job).

Cheers
John

If there is no access to a vertical mill can they be clamped vertically to an angle plate or fixture and cut with a slitting saw? maybe annealing the ends first to be kind to the saw.

Hi Perko

The MSMEE does not run training courses, however the monthly meeting is well attended if you live in Melbourne?

Visitors are welcome.

There are many other groups around Australia

**LINK**

Hi Martin

**LINK**

The Swiss company Fritz Studier Held one of the early patents. Now lapsed.
They used "polymer concrete" With their proprietary name Granitan using Ciba Geigy resin.

Polymer concrete is the description used by the Europeans, Epoxy Granite is used more on the other size of the Atlantic by the US

The reason for the break from Cast iron was not cost it was about the considerably higher vibration damping properties. The almost, and some say zero shrinkage of the cast after curing. and the advantage of being able to place steel inserts, pipework and other fittings within the almost cold mold. Casting accuracy of a thou .001" is not uncommon. Compare that to cast iron and the considerable amount of metal removal required to finish machine it.

On the con side it has a much lower tensile strength. You have to use thicker sections. and possibly for me anyway you have to rethink a project model to gain the benefits it offers.

For the home builder polymer concrete opens many doors. Form work can be just about anything; plywood, metal, chip board, plastic etc. Simple molds can be made for once only use or more durable materials for reuse.

And the rest of the world? See link below.

**LINK**




 

Edited By John McNamara on 26/11/2018 10:24:08

While i was preparing the transparent base image above I grabbed a couple of views that show the way the swarf guard blinds are set up

As can be seen there is not a lot of room available in this area after the Ball screw, linear rails, limit switches and cable chain are accomodated.

See earlier in the thread how the roller end brackets already laser cut are joined. aluminium swarf blinds are available commercially they have neoprene sealed joints to keep coolant out. Alternatively industrial heat resistant conveyor belting could be used, More investigation is required for the best solution at reasonable cost.

The belt is not rolled up it hangs down with a weight at each end, Rolling it up dirty I suspect would be problematic. A catchment tray is planned under the table. the rollers are sized for low cost skate board bearings.

The swarf guard blinds are supported by the top of the linear rails as well as at the edges, There is also a lip at each end of the table to keep swarf out. in combination with the blind the mechanism should remain pretty clean.

This is where CAD comes into its own, every part given its own space, and not much more.

Edited By John McNamara on 26/11/2018 08:20:27