Member postings for John McNamara

To learn lathework. milling Welding etc from a professional Abom79 on Youtube is a very good starting point, Most of the work he does is industrial so rather large but the same rules apply to the small workshop.

You can search youtube for Machinists to find many more... some good some not so good.

Hmm

Back to basics.....

Headstock spindle are the bearings tight with no play? Not much error there.

Headstock aligned to bed? turn a preferably thick say 25mm or greater diameter bar and check for taper? If the error is small the headstock is aligned to the bed with little error.

Facing test turn reveals a large error. Why? The cross slide is not aligned at 90 degrees to the bed.

I would remove the cross slide clean and replace it then carefully reset the gib for a nice firm but not overtight fit.

Do another test facing cut.

Regards John

Edited By John McNamara on 16/08/2018 00:41:47

HI All

Hmmm The Tea room, I was unaware of that room, I chose General I don't care where the post was started would have been happy to use the tea room. And no I don't normally mention Health issues to anyone. What I am glad to see is it raised awareness of an a malady that will affect so many people. **LINK**

It was the fact that there is a preventative measure available, a measure that I was unaware of and have paid for over the last 4 weeks which prompted me to post. Useful information that in my view should be passed on.

If my post offended you by intruding into the workshop space please accept my apologies and ignore the information.

Regards
J

Edited By John McNamara on 18/07/2018 07:57:53

Hi CB

Adding water beyond optimum is not a good idea. I am assuming you will be using ready mixed from a truck, The batch plant that filled the truck should have proportioned the water to the correct ratio for the mix strength ordered. it will make the mix easier to spread but it will weaken it. If it is really unworkable maybe a little water but not much. On high quality government jobs adding water is forbidden.

I hope the concrete supplier you are using is ISO quality control certified the larger concerns usually are this means the batch quantities should be traceable. Where I live there are a few rather gung ho mini mix operators. I suspect some of them batch by eye or is it by material cost? Best they be avoided.

At some point in time your new slab will crack. Another way of (Hopefully) controlling this is to get the top diamond sawed around 15-20mm deep with a grid pattern roughly 1 to 1.5 metre squares depending on the size. This will encourage the slab to crack along those lines You can fill the lines with acrylic sealer to stop dust settling in the crack. This is common building practice where I live.

Regards
J

Hi All
Look around you, one in three people are likely to contract shingles according to the stats. Well sods law and all that..... I kicked a goal.

The annoying bit is it may have been avoidable. there is a vaccine, ask the doc next time you visit.

WIth first hand experience I can assure you you do not want it, 4 weeks in and it is still most uncomfortable. At the beginning high power prescription only analgesics were needed. The good news is it is receding (hopefully but not certainly to zero) so all good there.

However all this would in 90% of cases have been avoidable,

Are you next?

Regards J

Every time i see one of Garry's new tools i am inspired by the attention to the detail and the many accessories, on this one right down to the finger grips on the tool body. Also the way the center point can be offset to completely turn a ball caught my eye. first class job.

J

Edited By John McNamara on 17/07/2018 04:47:33

Hi CB

The design of a slab and its edge and cross beams is determined by the type of soil it sits on. and the weight of the building it must support, however building weight is not normally the problem if single story. Soil stability is.
The edge and cross beams are normally taken down to clay or hard ground 5 - 600mm on sound ground with a clay base, but that is a just a wild guess. It depends on the site conditions, is there a layer of land fill? there will also be a spec for the correct reinforcing mesh. Remember concrete is borne to crack as it shrinks steel mesh is the only way to control but never stop it. **LINK**

Scalpings, sand, crushed rock etc will allow leveling a site but will not really help if the soil underneath them is low grade

see link re soil types UK **LINK**

The link above will not however tell you what is under your land, even if you are in the middle of one of the coloured areas. I have seen totally different soil reports under adjoining blocks in a street. I live In Melbourne Australia silty clay is commonly found, similar to parts of London.

Ideally an Engineer should be consulted to do the comps and prepare a specification. Yes this costs a little cash. Failing that maybe chat to a local builder that specializes in your area maybe over a pint your shout, A good local builder should know if there are any area specific problems to contend with.

You mention extending. If this means connecting an old slab to a new one is it important that the two remain perfectly level to each other after the toppings are applied? It is very likely that joint will fail and crack as new will move differently to old, The usual method is to drill into the side of the old slab and insert usually 12mm deformed bar pins into epoxy filled holes, you can buy the epoxy at builders suppliers. the rods then extend into the new concrete. That sounds like a fix and it may maintain a better joint but it is likely the level will not be maintained and one slab will move compared to the other causing a dip or bulge, this is caused by a change in moisture levels under the slab after covering and compaction of the disturbed ground. If perfectly flat is a requirement maybe think of replacing the entire slab.

I know this sounds like a lot of effort but we spend many many ours in our shed, It must be right.

(I am not a soil Engineer) I do however work with them as I did on site this morning discussing how to tackle an extension to an 1880 Victorian dwelling, yes the Victorians built attractive buildings however they knew very little about footings, as the often seen cracks prove. I see this time and again, Its a wonder they stay up, and it creates a lot of problems when modifying them.

Regards
J

Edited By John McNamara on 16/07/2018 14:15:06

Hi Andrew Hi All

Lathe Accuracy measurement.

I restored my lathe about 2011, At the time I was thinking on how to align the spindle and came up with the method I mentioned previously. As you can see below I used two dial indicators and a 25mm ground steel bar to check the spindle axis of my lathe. I had had not studied Rollie's method as I thought it related to twisted beds, a case of GMTA.

I attached the dial indicators to a temporary jig fabbed up from scrap and heavily weighted I wanted better control and no errors caused by the saddle that at that time was worn. I posted the fix here posted at MEW: Please ignore the preamble, all was and is OK. **LINK**

I also used a stretched 0.29 Metric piano wire and microscope to measure the 2.4mt between centres bed straightness. optically aligning the wire to a gap (It did not touch the gap) by eye, and reading off a micrometer
It gave repeatable accuracy to .0002", I think accuracy in Imperial! over such a long distance that sort of accuracy is better than many lasers.

If I had seen this paper recently written I would have tried it instead of the microcope
**LINK**

The CERN Accelerator is to this day mainly aligned by wire.

**LINK**

Images:
An Excel spreadsheet for one of the tests I did is below

Also a couple of images of a wire mounting point, there were 2, one at each end of the bed and the microscope stage kludged up from scrap and a 50 power student microscope, nothing hardened! just scrap It worked well. I don't have measurements it was done on the fly the v groves were just milled. It was however rock solid and sturdy. once adjusted the whole jig was clamped tight that is important.

Oh and a tenth accuracy Mitutoyo microscope head and a linear bearing formed the measuring stage that had to position the grove on center before a measurement was taken.

Also the precision counterweight used to hold the wire straight, yes it is hanging, you can barely see the wire in the photo! the gear is about 250 dia by 40mm thick. Amazing!

As it was a "one of" everything was done as a one off. Get the job done and nothing more.

The lathe bed was subsequently ground in situ, It worked well and I use the lathe to to this day, is it perfect? no, but almost. I do have a write up but too many pages to post here.

Regards
J

Hi All
As an alternative if you have a precision ground bar

25 – 40mm is ideal, of constant diameter say to
within ten thou and as well you have a tenth
accuracy dial indicator you can use these to check
the axis of your machine.

Just set the bar up in your chuck a 3 will do but
better a 4 jaw. Use the dial indicator to centre it. If
you have a 4 jaw chuck.

After cantering one point unless you are very lucky
the bar will not be in line with the machine axis at all
points. Also your precision ground bar may not be
perfectly straight, it does not matter! The dial
indicator is going to sort out any wobble in the bar.

We are going to take several measurements along
the bar, if it is say 300mm long maybe measuring it
ever 2cm would be a good start.

After setting up your dial indicator on the saddle and
moving it to the start point of your measurements
say near the chuck, and checking it is on centre you
are ready.

You will also need a ruler or other means to move
the carriage to the next measuring point.

Rule off rule off a piece of paper it will need 4
columns and as many rows as you have measuring
points. Mark the 4 columns; position, High, Low,
High minus Low

Now we are ready to find if there is any alignment
error between the axis of our lathe spindle and the
path travelled by a cutting tool at the diameter of our
test bar.

Before starting check again that the tip of your
indicator is on centre, and you are at the first
reading position 0.

Then rotate the spindle until the indicator reads
highest and note the reading on your paper in the
high column.
Then rotate the spindle until the indicator reads
lowest and note the reading on your paper in the
low column.

Repeat this for all the other positions.

At this point you have all the other highs and lows,
we can now calculate the error! Subtract the low
from the high and note the result in the last column.
You may get positive and negative numbers.

Repeat this for all the other measurements the
results will either be all the same (very unlikely), or
they will differ hopefully progressively, a straight line
error, you have a straight bed and saddle travel. But
the alignment to the spindle is out.

Alternatively the result will describe a curve this
indicates a straightness error in the alignment of the
saddle and bed as well as any overall error between
the alignment of the saddle and bed. On older
lathes there is often some error detected a dip in
the bed near the spindle is very common.

If you can use Excel you can do all this on a
spreadsheet and graph it.

This method does not check the alignment of the
taper in your spindle to the axis of rotation. However
this is easily done with a finger type dial indicator.

This method is a very good indicator of the
condition of any machine slide to spindle alignment.

To speed this process up fewer measuring points
can be used. Or for extreme accuracy more points.

Regards
John

Hi Neil

A mate who lives in Bright Victoria sent me this image. It was taken by his brother in Law while visiting with his astronomy gear. I gather it is the result of multiple exposures.

I find it amazing, I will put you in contact with the fellow stargazer If you like.

Regards
John

Edited By John McNamara on 25/06/2018 09:00:13

Hi Niels

Having used a lathe with a screwed spindle nose for a number of years, I acquired a new for me lathe with a DIN 5507 nose with a bayonet ring at the back. I would never go back to a screwed nose. I think the bayonet fitting is a better mount than a Camlock nose, Camlock's sometimes work loose.
The bayonet type is rock solid firmly bolting the chuck back face to the nose face.

Both Camlock and DIN 5507 use the same short taper. The only difference is nutted studs versus camlock pins.

Making up a new back plate is not that hard.
If you can find a name brand chuck already machined for the din taper it would give you a template to work from.

Link to types and sizes.
**LINK**

Regards
John

Hi John Olson

Use bring to front.

**LINK**

Regards
John

Hi All

Just search Google for a second hand copy. I noted several for 20-30 dollars. I have an eleventh and a 25th edition found second hand. easier to use than a PDF version.

Regards
John

Water jet works well however it has a few of caveats. The kerf of the cut is a lot wider than a laser particularly on thin materials under 10mm when compared to a laser, it is a little less accurate.

Where water jet comes into its own is cutting stone and ceramics, rubber and other plastics and plastic composites that will burn with a laser, also thicker brasses and aluminum over maybe 10mm depending on the machine, older lasers can only cut steel.

Water jets can also cut steel 50mm thick or when pushed at a cost up to 75mm thick. I have read of 300mm cuts in steel. That may be an old record!

In Melbourne at least where I live water jet is quite a lot more expensive.

Accuracy: Apart from the physical limitations to accuracy, comparing laser cutters to water jet cutters there is the machine programmer and machine operator to consider. Highly accurate cutting requires the machines to be operated at the optimum speed for accuracy, this will be less than the optimum machine speed for production. You should discuss this with the cutting service provider if extreme accuracy is required. It may be an extra charge.

Gases The gas mix used is also driven by cost factors, If you don't want a black edge on steel it can be reduced or eliminated by using more argon in the gas mix. together with slowing the machine down. again at a cost.

On the other hand most cutting services I use quote around +-.1mm maximum error in 5mm steel. There is no point in paying extra if it is not necessary.

To put .1mm into perspective If I make a rectangular hole in 5mm plate say 20.1mm x 5.1mm and make a tennon on the edge of a plate 5mm x 20mm then most of the time I will get a drop in fit. There will be a tiny radius on internal corners. This can be overcome by drawing in small relief areas not necessary for me I just touch them up with a tiny file. To a modern laser 5mm - 12mm plate cuts like butter. As plates get thicker the accuracy reduces slightly.

Normally I will have multiple tenons on an edge fitting into into multiple rectangular holes for bolting or welding Every time I do it I am amazed! They all fit....

When getting a job quoted your job will cost less if you provide a clean DXF file for your part. If your CAD can draw closed polylines use them for all plat outlines and holes. Make sure lines are not elevated above zero if your program can do 3D. If just using lines make sure that every line end touches the next line exactly. Closed polylines make this easier. No line should have a loose end when making a hole.
Before you start ask the cutting service how they want the files presented. If you don't use or have a friend that can use CAD.
Some cutting services will do it from an accurate paper drawing but there will be somewhat a hefty charge.

Edited By John McNamara on 02/06/2018 06:50:49

The old rule of thumb is the hole should not be smaller than the material thickness, As I said the old rule. These days newer machines can make smaller holes than the material thickness. Fiber lasers in particular and the latest CO2 machines. Ask your cutting service what they can achieve.

I have a 4 way tool post on my lathe, two of the stations are fitted with two eccentric engineering tangential holders one fitted with a high speed steel bit the other I made from medium carbon steel with a carbide tip l brazed on by me. In both cases I find that the quality of your tool grind finish is very important. Since I switched to a fine diamond cup wheel that gives a mirror finish my work finish has improved and the time between regrinds greatly increased.

I still find that HSS with a razor sharp mirror grind beats carbide almost every time for finishing to size, it allows you to shave down to a tenth or so where carbide will simply rub.

The carbide tip works well with harder materials that HSS will not cut and for high speed metal removal that would burn HSS.

I made my own grinder **LINK**

however any grinder that can be fitted with a table that can be angled and a diamond cup wheel will do.
Apart from the wheel accurate relief angles are very conducive to better work finish and accuracy.

I think the angled sides are a clue. Maybe a jig for grinding facets on some sort of cutting tool?
 

Edited By John McNamara on 11/05/2018 14:49:20

This week I had to drill axially centred 1mm x 70mm holes in some cast iron scrap bar. (window weights) It machined easily so all good. Well almost when I drilled it axially the drill wandered a bit maybe 20 thou, something had deflected the drill. hard spot, soft spot, who knows? In this case it was Ok as I was able to machine the outside of the bar after I had drilled it using the hole as a center hole. It was not a super precise job. I had used a normal jobber drill, and it had got the wanders

This is where Gun drills differ, they often only have 1 cutting lip the rest of the drill is a solid cylinder several diameters long that has almost no clearance. fully supporting the cutting tip apart from a chip clearing groove. They usually have a cutting oil hole pressure fed to clear the chips, The tight fit in the hole helps keep them straight, think of a gun barrel maybe thirty inches long with a .177" finished hole with little or no straightening required, pretty amazing.

Regards
J

Yet again James Virgil Howe to the rescue

There is a whole chapter on making gun drills,

Could you source a piece of 20mm dia High speed steel? Maybe a worn endmill, you can machine it with carbide.
Howe had to produce tiny grooved tubes, not easy. 20mm makes things very easy.

**LINK**

Regards
John

Edited By John McNamara on 10/05/2018 00:01:27

Hi Editor Neil

A number of the scanning devices don't open bound books more than 90 degrees, about the same as if you were reading them. Keith Rucker at Vintage Machinery is compiling a free database of mainly American Machinery. He made a video of how he scans Books and brochures.


Regards
John >**LINK**