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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: myford Ml7 lathe problems
20/12/2015 20:51:54

Removing and replacing a workpiece in the chuck is just about guaranteed to put it in a different and non centred position. That is why most people will say machine all features that need to be concentric without removing the part from the chuck.

I do not know what material you are practicing on but some steels will always give a poor finish. In the meantime make sure you are working with suitable feeds and speeds for the material. It is easy to be too aggressive or too timid when you have no experience. Published values are a good starting point, adjust slightly to see what different values have on finish.

Martin

Thread: What did you do today (2015)
20/12/2015 20:38:34

No option to right click when using a tablet touch screen.

Martin

20/12/2015 12:22:04

Neil, is it an analogue computer? I have vague recollections of something looking like that that demonstrated some aspect of finance.

Martin

Thread: Stirling Engine : Laura
20/12/2015 10:35:35

I would not be too worried about the diameter where the o ring fits. If it is snug on the cylinder and trapped between two other parts then it will do its job. If however it does need a accurately sized diameter then consider soldering in a ring to machine back to size. It may require a little more machining off the recess before the ring is soldered in depending on where the join line falls.

Martin

Thread: Spindex End Mill Sharpening
19/12/2015 21:44:39

A hacksaw blade may be too stiff. A feeler gauge blade may be a better option if your flute stop is a short one.

Martin

Thread: Siemens Micro Master 150 for ML7?
19/12/2015 15:33:47

If you can get hold of a 110V site transformer you can start off with an isolated lower voltage. You may also find that the voltage between one pole of the output and the earth point is 55V. If you do not understand electrical circuitry get help from someone who can look at these posts and knows what to do.

Martin

Thread: 120mm diameter Delrin machining problem.
19/12/2015 09:07:25

It is easy to melt when drilling. The other problem I have had is that the hole closes down on the drill after the point has passed. Even with a new drill the material moves out of the way rather getting cut by the sides of the drill. The deeper you go the greater this drag on the drill gets and the more the heat builds up. Take the drill out frequently and check it's temperature, cool it with suds as well. Low speed high torque is best for larger sizes.

I found drilling partway with small drills then opening out that hole with larger drills up to the required size before drilling further using the same process kept the friction under control.

Martin

Thread: 4 Jaw Self-centering Chuck runout problem
19/12/2015 08:53:31

I would not use the outside of the chuck as a guide to how well it has been mounted. I would find exactly what the TIR is close to the jaws and also 50 to 75mm away from the jaws. If there is a significant difference between the two I would be looking at the angle the chuck has been mounted at. There may be contamination in a joint somewhere that needs removing. If the readings are the same then there is an axial displacement. As Rod said check the jaws are in the correct slots if it is marked 1 to 4. If not try rotating the jaws around the chuck to see if one position gives a better reading than the rest.

Most chuck mounting involves a register or two (lathe spindle and chuck backplate) to correctly position the chuck and to do so repeatedly. Does you setup have suitable registers and if so what is the run out on them?

Martin

Thread: Stirling Engine : Laura
19/12/2015 08:39:43

Not sure what you mean by sitting right, the flats on the bar will set the insert to the correct angle. You may need to set the tip slightly above centre line though. I would also suggest a bit of packing on the top face of the bar, it will quickly get chewed up by the clamping screws otherwise. Boring bars need to be set to the minimum necessary stick out for the job being done. This means a lot of clamping and releasing to damage the bar if not protected.

If you are using a boring bar with an insert close to the minimum diameter it will fit in you need to look at where the bottom corner of the insert is to make sure it is not rubbing, this is why the tip needs raising sometimes.

Martin

Thread: Doncaster loco green?
19/12/2015 08:16:20

You must understand that any picture you look at on a computer, in a magazine or anywhere else will not be true colours. If you doubt this put two monitors onto a computer and straddle the screens with a picture. I can guarantee that the monitors will display colours differently. If you want authenticity then the paint chips are the only thing likely to be correct. If you want it to look how you want it to look then mix your own colours.

Martin

Thread: Steel brick
18/12/2015 18:53:02

Location always helps with a request like this.

Martin

Thread: Duchess of Sutherland
18/12/2015 18:49:08

I also dislike what is becoming a common grammatical error. The crowd was an "amount" of people. It should be a "number" of people. 50% is an amount and 100 is a number.

Martin

Thread: lathe chuck key hex
18/12/2015 14:32:30

Can you get a chuck key with a square over 14.66mm across the flats and machine or grind it down to 1/2" hex?

Martin

Thread: 120mm diameter Delrin machining problem.
18/12/2015 14:15:21

If you have enough material then you can use a hacksaw to cut three sections out at 120° intervals around one end to leave a triangular end for gripping in the chuck. Turn the other end down to a diameter to suit the chuck then reverse and machine where the three cuts were made. If you are going to machine away a lot of one end then you are only cutting away material that would become swarf anyway. Without knowing exactly what the finished item will look like its hard to know how good any of these suggestions are but hope these two ideas (mine and Andy's) help.

Martin

Thread: Syncing up Arduinos
17/12/2015 18:58:50

It is less of a problem using old leadscrews on a lathe than on a mill because almost all working motion is in one direction only. Having said that I did replace my cross slide lead screw with a ballscrew. I did this without modifying the lathe so I can always return the machine to the as built parts. I wanted to be able to do curves as needed for ball turning with minimal backlash. I put a ballscrew on the carriage with just one M6 hole drilled and tapped for the connecting bracket. I also put one M6 hole in the end plate of the headstock for a spindle sensor but this is hidden under the cover. All other mounting uses existing features on the lathe. It may not be pretty but it works.

Martin

Edited By Martin Connelly on 17/12/2015 18:59:55

Thread: Avoiding stuck chuck - intermitterent cuts
17/12/2015 17:01:33

Using the motor to spin the chuck backwards in direct drive runs the risk of damaging the mechanism that locks the pulley to the spindle. I have not stripped my pulley down to know how strong it is but it may be less strong in reverse than forward. Damage here may be more trouble than broken back gear teeth. If I had a really stuck on chuck I would find a way to lock the spindle where it sticks out of the back of the headstock to avoid stress anywhere inside the headstock.

Martin

Thread: Syncing up Arduinos
17/12/2015 11:38:59

I second John Haine's comment. Most of the cost of these projects is now in the stepper motors, stepper motor drives, controller board and power supplies. I have two old laptops that were gathering dust running Mach3 to do CNC on a Smart and Brown Model M and a Rong Fu mill. The laptops effectively had zero cost because I already had them. They only have to run XP with no background programs that use up processor power and most of the work is done in an external processor (Smooth Steppers in my setup). Anything that uses something like an Arduino will share most of the cost of a CNC setup because a lot of the hardware required is common to each system. With CNC you do get the option for a lot more functionality than an Arduino setup that is only good for one thing such as threading without change wheel swapping.

I have no problem threading with Mach3 because the limitation is in long threads which I have never had to do. The single pulse per rev of the spindle is also fine for me since I run my lathe using backgear for threading so the chance of the cutting force slowing the spindle down and causing problems is very close to zero (3Ø vfd driven 2hp motor)

I really like the option to set feeds to a per revolution value when using manual data input (MDI) so using the machines in a manual manner without a CNC part program to be seen. Very useful when parting or grooving to get a steady feed rate.

Martin.

Thread: Off center groove
17/12/2015 09:04:36

Clamp it to a lathe faceplate with packing under one side to give the required angle. The clamping will need to be in the centre hole, you may need an intermediate plate with suitable threaded holes in it. If there are a number to be made make the intermediate plate into a jig. There will be a slight variation in depth of the groove due to the angle of the work piece. Centering will have to be done carefully as the od will not appear to be round when mounted at an angle.

Martin

Edited By Martin Connelly on 17/12/2015 09:05:48

Thread: Cutting Internal threads
17/12/2015 08:08:09

p1080941.jpg

17/12/2015 08:07:50

Ady1

I have one of those pre-insert days external threading tools marked up as Eskilstuna - Sweden. I will upload a photo and post it. The circular die is about Ø42mm so it would be hard to use for any small internal threads if a suitable holder was made. It has a screw at the front for small adjustments to the stick out and the head can be swiveled on the body to allow for different helix angles. As I say it was pre-inserts. I think they have been replaced with throw away inserts now. Reduces the need for someone to sharpen it and then for the tool to be re-set.

Jon

I have a thread milling tool I made with Horn inserts in it. Could be used for internal threads if there is a big enough bore.

You can see it in action here.

**LINK**

Martin

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