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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: RPM counter for Myford Super 7
09/08/2016 09:13:07

Richard, XV408? It was at Coningsby when I was there.

Martin

Thread: Depth Micrometer Head
09/08/2016 08:58:45

There are some Mitutoyo 0-25mm depth gauges on Ebay at the moment.

LcAAOSwHoFXqMMm">http://www.ebay.co.uk/itm/Mitutoyo-0-01mm-Depth-Gauge-Japan-/162163000412?hash=item25c1ab045c:gLcAAOSwHoFXqMMm

**LINK**

Plus others. Just search Mitutoyo depth for a selection.

Martin

Thread: Serial Taps
01/08/2016 19:08:39

Typical depth of thread should be close to one diameter. You should not normally be tapping over 12mm for a M6 thread.

Martin

Thread: Electronic ignorance
31/07/2016 15:51:23

I think a good book for a beginner is Electronics Pocket Book by E A Parr.

ISBN 0-408-00481-9

http://www.sciencedirect.com/science/book/9780408004817

The link will let you look at the first page of each chapter to see if it is what you need. 

Martin 

Edited By Martin Connelly on 31/07/2016 15:59:23

Thread: tap, die charts
28/07/2016 15:18:31

The British Standard for metric threads has a deviation from nominal for class e fit (the sloppiest fit) for a pitch of 1.75mm of -71 micrometers so not far off Thor's 0.1mm figure.

Martin

28/07/2016 15:02:34

Tapping size for metric is nominal size minus pitch. eg M6x1 is Ø5mm. In reality Ø5.1 will be ok as well but easier to tap.

Martin

Beaten by one second!

Edited By Martin Connelly on 28/07/2016 15:03:18

Thread: Milling facility on my Myford ML7?
28/07/2016 14:58:37

I bought one of these at work for positioning items under a dot matrix marker.

**LINK**

It is well made and suits the purpose it is being used for here. For milling it may be too weak for working with steel. The problem with the material it is made from is that it is easily marked and I can imagine getting some debris into the slides and causing damage. Cast iron will be far more resilient. The leadscrews are not acme style, just basic 60°. The leadscrew nuts are short and made of brass, the operating knobs are plastic and there is no way to reduce backlash without modifying the table.

I would look for a suitable cast iron option.

Martin

picture1.jpg

 

Edited By Martin Connelly on 28/07/2016 14:59:30

Thread: is this motor suitable for a milling machine
26/07/2016 18:41:36

Mark, the wiring is quite easy based on your photo for low voltage. Join together L1, T1 & T7. Join together L2, T2 & T8. Join together L3, T3 & T9. Join together T4, T5 & T6. To do this you need a connector block with four terminals that can take two cables in one side and one in the other side.

Martin

Thread: Downham Potentiometer
26/07/2016 13:41:30

I've seen old pots that do not have the wiper as the central terminal. I would do as Bazyle suggests and find out which terminal on each pot is the wiper and make sure the cable from the original wiper terminal is on the new pot's wiper terminal.

Martin

Thread: is this motor suitable for a milling machine
26/07/2016 13:33:13

I'd use a rigid type terminal strip rather than the soft nylon type, they are more like the material usually found as terminal blocks in motors and may be more resilient with regard to fretting due to vibration.

**LINK**

Martin

Thread: tapping drill
25/07/2016 08:46:34

Lathes.co.uk has a section on fitting a chuck and making a backplate for a screwed nose spindle. The part about register accuracy is interesting to read.

**LINK**

Martin

Thread: WM16 Advice
24/07/2016 21:27:25

Try searching G0758 cnc. This is a similar machine from Grizzly in the U.S

Martin

Thread: Rust and corrosion solutions?
24/07/2016 18:52:07

Process tanks for mild steel that used to be in the place I worked had phosphoric acid sold as deoxidine by ICI followed by a plain water rinse then a hot dunk in a solution of sodium nitrite. The heat of the tank heated the steel so that the water flashed off when the items were removed from the tank. If the treated parts were not going to be painted they were given an oil spray for longer term protection.

Martin

Thread: Moore and Wright Value Series
21/07/2016 19:51:35

I'm with KWIL on this. Mechanical calipers work every time and the zero never moves.

I have trouble getting digital calipers to give the same reading twice in a row. Mechanical vernier calipers with thumbscrew drive give repeatable results that match micrometer readings. The rolling thumb drive on some digital calipers make it hard to get the same pressure for every reading. I only use digital calipers for rough guides, I also worry that the risk of using them with the zero set wrongly is too high for parts with a lot of time invested in them.

Martin

Thread: Beginner needs help with Colchester Bantam Lathe
19/07/2016 11:53:01

The forward/reversing switch should energize the coil and should not go to com2, com2 should be wired directly from A1. You do not seem to have a 24V control system so you need a contactor that has a coil designed for mains voltage. One side of the coil is connected directly to the C1 terminal and the other side to A1 through the forward/reverse switch. You should only have the two wires going to the reversing switch. Put the wire from A1 to the common terminal of the forward/reverse switch. If you find forward and reverse are the wrong way round then swap the wire going to the coil to the other terminal of the forward/reverse switch.

Martin

Thread: Aircraft General Discussion
17/07/2016 19:03:02

BBMF Lancaster took to the air for test flight today following post fire repairs.

Martin

Thread: Tool Holders for Dickson Clone
17/07/2016 08:44:40

Clive, if you do the calculations of forces on a morse taper you find that when the tan of the angle (I can't remember the exact details) is less than the coefficient of friction the taper is classed as self holding. However the self holding force is easily overcome by additional force such as used to eject the tapered item from the socket. I think there are similar forces involved with these tool holders and they are relying on friction. Given sufficient force this friction will be overcome as well. That is why I made a new plunger to take the holder closer to a mechanical lock. True mechanical lock would require the cam to be at tdc but would also mean perfectly sized parts all round. That is why I aimed for close to tdc. At this point the pressure point on the plunger will be close to the centre line and the force required from the plunger to turn the cam will be very high. With only 90 degrees of motion to the pull up point the contact point between cam and plunger will be off the centre axis and the force required to overcome friction and turn the cam much lower. If I remember correctly it only took a couple of hours to drill and turn the new plunger so I think it was a small investment of time to get a better tool holder clamping action.

I think the off centre pressure point means that the plunger may twist anticlockwise when viewed from above. This would put all the pull up force on the tool holder on one lip and that is the one furthest from the workpiece. This is the worst possible result mechanically which is why the idea of the pressure point close to the centre line of the plunger seems much better to me.

Martin

16/07/2016 21:31:30

I think the cam needs to rotate to near the top dead centre to give the best chance of locking the holder and for the best mechanical advantage in the pull up. If your cam is a long way off that best position then you do not have the best possible grip on the tool holder. The pull is off to one side and the forces acting on the cam will be able to rotate it to the release position.

Martin

16/07/2016 13:48:53

Michael, what angle does your cam rotate from fully out to locked? Mine originally only turned about 90 degrees. I put a clock on the part that pulls the tool holder in and checked how much movement there was from the locked position to the fully retracted position and it was 1.25mm. I then made a new one of these parts to pull the holder that was 1mm longer from the hole to the working face. This allowed the cam to rotate close to 180 degrees and gives a much more positive clamping and locking action. This is possibly the problem with clones, what is probably a critical dimension is wrong on some of the clones. It is a relatively simple part to make so might be worth a try to see if it stops the holder coming loose in use.

Martin

Thread: Beginner needs help with Colchester Bantam Lathe
15/07/2016 20:24:39

To reverse this motor use a double pole double throw contactor. Each pole will have common, normally closed and normally open terminals. COM1, NO1, NC1, COM2, NO2, NC2. Connect U1 to COM1, U2 to COM2, Z1 to both NC1 and NO2, Z2 to both NO1 and NC2. In this setup with the contactor de-energised you will get CCW and energised you will get CW. A second run contactor is used to apply power to the reversing contactor common terminals.

Martin

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