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Member postings for Martin Connelly

Here is a list of all the postings Martin Connelly has made in our forums. Click on a thread name to jump to the thread.

Thread: Basic DRO
28/12/2021 12:41:58

The thing about extra features is - you don't have to use them. They will not interfere with doing what you want one to do and they are added because once the basic mechanism and display are set up the extra few buttons and software do not add much to the production cost. However not having them will allow competitors to claim bragging rights and so get more sales.

You will best be served by concentrating on what you need such as reliability, size, accuracy, ease of fitting and doing what you want it to do and not worry over extra features you will not use. If you think about software such as CAD, word processors and spreadsheets who uses all the available features? Probably close to no-one, it doesn't stop anyone from using these programs for what they need them for.

Martin C

PS one of the features often available is to chose diameter or radius. It is useful even if most of your turning is based around diameters. You may want to do things such as gear cutting, drilling or even milling on your lathe where a DRO set to radius would be more useful.

Edited By Martin Connelly on 28/12/2021 12:45:14

Thread: Middle of Lidl
27/12/2021 16:07:47

I see that one of the items that will be available this week in Lidl is a 107 piece set of coated HSS drills in 14 sizes Ø1 to Ø10 for £14.99. They may not be top grade but for pilot holes or general use they will probably be fine based on other Parkside drills I have had. Possibly worth buying to keep the better drills for when you really need them.

Martin C

Lidl drill set

Thread: Speed Camera Flashes?
27/12/2021 15:58:37

If you do the calculations you will find that exceeding the speed limit doesn't save enough time to make it worth the risk. Quite often I find that I catch up with people who have sped off in front of me as well since they get held up by traffic just up the road.

I live in a village that is about 1/2 mile from entering to leaving and has a 30mph limit in the village and 60mph limit on all roads in and out, To go that 1/2 mile at 30mph takes 1 minute. To go like a bat out of hell trying to do 60mph will cut the journey by 30 seconds. If you go at 40mph will save you 15 seconds. In my mind that time saving is just not worth the risk to people, pets or property.

If you go a long way on a motorway or dual carriageway the time saving will still only be measured in minutes if you go at 10% over the speed limit. Set off earlier if you want to get there sooner.

The other thing to think about is how many cars have a dashcam these days that record location, date, time and speed. Combine that with the increase in the number of police forces that now allow dashcam uploads for them to look at and decide if they want to prosecute. All it takes is one disgruntled driver to report you and supply dashcam recordings and you could be getting a letter in the post.

Martin C

Thread: Minimum bending radius
26/12/2021 09:12:33

The bend radius you can achieve depends on how you bend it, supported or unsupported internally, as well as wall thickness, outside diameter and material.

This was the cardboard computer I used at work to decide what tooling needed buying if a new part was designed outside of the existing product designs.




I can't find it at the moment but you can figure out from the pictures what would be possible for an unsupported bore. Beyond that there are a number of ways to support the internal bore to avoid wrinkling that have been covered in a number of threads.

Martin C

Thread: Myford vfd
24/12/2021 16:36:32
In YouTube select share then embed then copy. In the forum when posting select the YouTube Icon and paste into the box, edit the pasted data to width 450 (I also set height to 253)
Martin C
Thread: Guided bus lane
23/12/2021 16:34:33

I am not greatly in favour of ambulance chasing but if you were injured or traumatised in any way or otherwise had costs beyond what your car insurance covered then there is a clear case for a claim here if the HSE thinks there is a health and safety failing.

Martin C

23/12/2021 14:47:19

I have recently been to Stanstead to drop off and subsequently pick up someone who was going on a flight. The drop off only carpark has barriers and automatic number plate recognition systems that have been in use for years and work well. Surely it would have been far more sensible to have a similar system for the guided bus lanes, only open the barrier for registered numbers. That way they would not need the car traps that not only cause damage to straying cars but also effectively close the bus lane until the car is removed. The additional risk to cyclists and pedestrians who may be on it, legally or not, is also something the HSE would take into account. I remember a case where a company was fined when some boys who were on a roof fell and were injured. The company were fined for not preventing the injuries suffered by preventing access to the roof. One of the results of this was that all access ladders to roofs, cranes or platforms where I worked had hinged panels fitted over access ladders. The panels were padlocked shut and the keys held by the plant department.

I looked at the news report and it is a temporary closure to be in place until the HSE are satisfied there is some risk reduction carried out to their satisfaction. They did not state what the risks being looked at are but an uncovered hole where people may be driving, cycling or walking will be a big no no for the HSE.

Martin C

PS I think anyone who ended up driving on the bus lane and ended up with their car in the hole should speak to a lawyer regarding compensation from the relevant operator based on the health and safety failings that are clearly of concern to the HSE.

Edited By Martin Connelly on 23/12/2021 14:51:26

Thread: DRO's and mental agility
22/12/2021 11:27:00

There has been some data that "Brain Training" actually does very little to improve the brain function over time. The thing about DRO systems is that it is just a different way of working that still requires the use of the brain, just in a different way.

The advantages of a DRO system is that you don't need to count turns on a handle and that you also don't need to do as much (if any) marking out for simple parts. Two of the biggest advantages are the ability to switch between inches and millimetres as required so it no longer matters what initial units your machine was designed for and that backlash no longer has to be taken into account when turning handles. One caveat to the above is that threading metric pitches on an imperial lathe and vice-versa is still as much of a pain as always.

The other time a DRO will be useful is if you add power feed to an axis. If it is set to rapid traverse then trying to count turns of a handwheel is a near impossible task if the handwheel is just a blur.

I think to some extent the people who have home workshops can't be lumped together into a single type of person who enjoys their hobby in the same way that everyone else does. Some people like to restore old machines to an as original state as possible and the idea of adding a DRO would make them wail. Some people will take the view that they will make full use of all modern conveniences as the journey is not as important as the destination. Between these two views there is a spectrum of wants and needs. That's why questions like the regular "what mill or lathe should I get" end up with so many different responses. It would be a boring world if we were all the same.

Martin C

Thread: Maths problem just for fun
20/12/2021 11:16:13

The hole through a sphere was one I expected to appear here. I remember the solution as stated above but at the time I first came across it the solution was a bit above my maths education level.

Martin C

Thread: Another workholding problem
19/12/2021 15:29:16

Hold the OD with a 3 jaw chuck. Machine the inside bore undersize and leaving a lip. You can then use this inside lip to clamp the part to a faceplate or other flat plate. Machine the outside features and the holes. Then use the outside lip to hold it on a suitable plate to bore out the centre to size.

Martin C

Thread: Maths problem just for fun
19/12/2021 15:11:10

I got 4.701kg for the three holes in the block problem. The hardest part was visualising what was left in the middle. What is taken out of the centre is a 50mm cube less eight pointy corners with the three curves on them and six Ø50 cylinders 25mm long. The pointy corners have a 7.322mm cube in them. The three times eight points were the problem that then needs calculating. Once I figured that these points had a square cross section it is relatively easy to do an approximate volume by slicing them at 1mm spacing from the point (0.1 to 17.1mm since 17.1mm is 0.5mm less than the point where the internal cube is in these corners) and calculating the size of the square (Pythagoras again) and summing the areas of these squares.

The numbers (in cubic centimetres) come out as follows:

Original volume 1000

Six cylinders to remove Ø5 x 2.5 = 294.524

Central 50mm cube to remove = 125

Eight 7.322mm cubes to put back in 3.14

24 points to put back in 3.998

Total = 1000-294.524-125+3.14+3.998=587.614

The weight is then 8*587.614=4700.912g, 4.7kg

Martin C

18/12/2021 13:10:33

Rob, farmer Giles needs a tether at least 25 yards long just to get the goat to the centre of the field and that is clearly not going to let it graze half the field. The actual required length is a smidgen under 29 yards. You have to get a formula for the sector that the tether gives access to then a formula for the two edge segments that need adding to this sector to give the total grazed area. It's just a bit messy needing pi for areas, inverse cosine (or inverse sine depending on which angle you chose to calculate) for the sector angle and Pythagoras as well. Then solve for this formula equalling half the total area of the field.

Martin C

17/12/2021 19:08:31

Duncan and Rob, you are correct it does come down to a quartic equation. Using similar triangles and Pythagoras' equation if you take the base of the ladder to the near corner of the box as y you can show that the top of the ladder to the near corner of the box is 4/y. The quartic equation is y^4+4y^3-92y^2+16y+16=0. Luckily I still have my trusty Texas Instruments TI-68 which solves quartic equations and gives the following values for y: 0.521036706, 7.677002321, -0.33724556, -11.86079346

The two negative numbers do not work as the top of the ladder will be 2+11.86 above the ground and requires a ladder 14.06 feet in length. The other two give the answers that work. x equals 2+7.677002321=9.677002321 or x equals 2+0.521036706=2.521036706, the latter being a bit silly.

Somewhere I have got a spreadsheet I did that solves polynomials using the matrix method that I put together just to see how well it worked.

Correction, solves simultaneous equations, not polynomials,

Martin C

Edited By Martin Connelly on 17/12/2021 19:10:10

Edited By Martin Connelly on 17/12/2021 19:46:52

17/12/2021 12:57:55

There is one other method of solving the resistor cube. It involves splitting two of the resistors into two in parallel 2ohm resistors. Then the cube can be split into two mirror images with simple series and parallel paths to calculate. Calculate one side then half the value (parallel sum of the two sides) to get the final answer.

Martin C

16/12/2021 13:08:11

This is my take on the solution. It requires solving the equation to find angle alpha using trig identities which I did not include on the page as it is messy and seems a bit unnecessary to show here. The point is it gets the same result a different way from those above.

p1160224 (2).jpg

Martin C

Thread: Drilling brass.
14/12/2021 08:55:05

I have had a screwed shank Ø6 end mill unscrew from a Vertex Posi Lock chuck when working with brass. I only figured what was happening when I spotted the end mill suddenly stop rotating with the chuck just for a moment as it dug in and was screwed back in. I had to resort to pre-loading the end mill into the chuck, lots of discussion in threads in this forum about how these chucks should be used and pre-loading is not usually recommended. For large holes in plate I find broaching cutters are good but a hole saw may work if you can clean up the hole afterwards.

When I was at work there was a lot of copper bus-bar drilling. We had to use drills specifically designed for use on copper (Dormer I think) because of the grabbing of standard drills. I don't think you could justify the cost unless you did a lot of same sized holes in copper or brass.

Martin C

Thread: Boley 8mm collet nut
08/12/2021 10:51:42

If you find you need to hold small items in a 4 jaw chuck an ER16 chuck on a parallel shank will work for a lot of the things you want to do. You haven't said what the target sizes are but I suspect the collets you are trying to make use of are for specific diameters and may go smaller than the ER collets but the ER collets would add to what you can do with your 4 jaw chuck and existing collets. Something to consider in the future maybe.

Martin C

Thread: How can I convert a 0.5 inch benchtop grinder to take 1inch wheels?
07/12/2021 17:46:56

You can get plastic adaptors to suit most common bores and arbors for this purpose. Try searching for grinding wheel reducing bush.

Martin C

Edited By Martin Connelly on 07/12/2021 17:47:08

Thread: Aluminium Stick of Rock?
06/12/2021 19:54:06

A lot of bar stock starts off as continuously cast billets. There are tun dishes at the top of the moulds and they are topped up from large ladles. It is possible that when there is a topping up operation dross on the surface is pushed down towards the mould by the flow of the fresh liquid metal being poured. I can imagine this dross getting into the centre of the cast billet. I don't know if this is used for aluminium since it starts off as slabs that are formed by an electrolysis process but it is certainly used for steel. Plenty of YouTube videos about the process.

Martin C

Thread: Drilling and filling of the Dental kind.
03/12/2021 16:06:14

I think my dentist has 2 receptionists, 2 dental hygienists and a dental nurse. So as well as costs for equipment, consumables, business rates, rent, probably an accountant, electricity, business loans to repay, there are six people's wages included. It soon adds up. All these costs have to be paid for out of the 40ish hours they are working per week since they cannot run shifts or let automatic processes run through the night. They also have to clean and sterilise the treatment rooms between patients.

Martin C

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