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: Tool post grinding|
Does anybody know if a Dynafile/Dynabrade type machine has ever been put to use as a tool post grinder?
|Thread: Cutting Speed Table|
You may have no intention of getting into CNC at any point but it may be worth downloading Mach3 onto a computer. This has a wizard for speeds and feeds for milling included in it. It can be run in demo mode without a license (just select no device when asked when it runs) but the wizard works fine. Just make sure you have selected the correct units (mm or inches) in the config settings and close the program to set the units then start it up again.
To use the table that started this thread your cutter is Ø20mm and the material is aluminium. This gives a speed from the Ø19 line of 1006rpm. Consider this a maximum speed if you have a machine with enough power at this speed and choose something close to it eg 1000rpm would be fine but lower would also work.
What this table does not tell you is feed rate for milling. It is important to keep the cutter cutting not rubbing as earlier posts have stated. If we take the rpm to be 1000 for ease of calculation then we need to look at tooth load and number of flutes on a cutter. Let's go for a tooth load of 0.125mm or 0.005". First we can consider two flutes, this will give a count of 2x1000 = 2000 teeth per minute at the cutting point. In order to give a tooth load of 0.125mm we need to multiply the teeth per minute by the tooth load and we get 2000x0.125 = 250mm/minute as the feed rate. If we put the figures in for 4 flutes we get 500mm/minute as the feed rate.
So if you want to cut at the correct tooth load with a Ø20 milling cutter with 4 flutes you need to feed the material past the cutter at 500 mm per minute or 20" per minute.
Can you achieve this? It will depend on your choice of hand cranking, power feed or CNC on you machine. If you are hand cranking I think you should time yourself over a suitable distance to get an idea of the speed you need to go. Similarly if using a power feed you should find what speeds you get for the available settings. Using smaller cutters with higher rpm will require even faster feed rates.
One other thing about cutting aluminium is the risk of aluminium welding itself to the cutter resulting in built up edge. **LINK** This is why some lubrication is necessary and avoiding excess heat from rubbing helps.
|Thread: CNC controller problem|
I do not switch the motors on my vacuum cleaner or compressor on or off when I am running a CNC program because it always causes the CNC to freeze. This is an electrical noise problem. I think you need to move all of your motor wiring including its supply point as far away from the rest of the system as possible. I start and stop the mill motor manually but it is a vfd driven 3 phase. The switch for this is only a low voltage system and the motor runs up and down under electronic control without current surging in the wiring.
Is you motor wiring shielded? Is the motor power supply going through a spike suppression filter? These may help.
This is the type of power suppressor I am thinking of.
Edited By Martin Connelly on 22/04/2017 08:16:54
|Thread: 3D printing step forward.|
Siemens printed turbine blade video. They do not have the life of the current blades but it will allow rapid development compared with the 2 years it takes at present to prototype and test new designs.
|Thread: Boring copper tube problems|
I've found rendered pig fat in the form of lard the best lube for rise and fall brass door hinges. I tried all sorts of other thing before lard but none worked as well.
|Thread: Checking lathe alignment?|
I have had to work out the sag on very large arbours for reverse alignment years ago. I also wrote spreadsheets for calculating the machining of spacer shims to go between turbine and generator underbases from the resulting figures. Lasers alignment has made alignment so much easier. I gave a small machine optical alignment kit to a local astronomical society for use as spotter scopes rather than scrap it off when we started using lasers.
The empirical method for finding the sag on a support arm or arbour was as follows.
With the arbour resting on the floor use a spring balance to find the force needed to lift the free end of the arbour off the floor. Clamp the arbour securely to something solid and vertical (we used building stanchions) then put a suitable indicator underneath the free end and set to zero. Apply the force needed to lift the end found earlier and note the deflection of the indicator. stamp this value on the arbour for use when doing reverse alignment.
These arbours were often well over 1 metre in length.
|Thread: Gear size|
I misread the original post, I thought the tumbler was the 34 tooth gear. A 30/34 combination added into the drive train would correct the error from the larger gear on the spindle but this additional set of gears would require the tumbler to be used in the reverse position for normal forward motion. You would also need to add a mounting for it.
If it just acting as an idler then none. Think of it as one tooth on the spindle moving the tumbler one tooth around. The result is the first driven gear moves around one tooth regardless of the number of teeth on the tumbler.
|Thread: U-Profiles from Square Tubing|
If the length is not too great you could push a piece of 12x12 wood into it for support. Just cut one side at a time and only deep enough to cut the metal, not the wood.
|Thread: P-Power hacksaw|
Windscreen wiper motors are continuously rated but the question is what is the rated power for wiping windows. If you slow it down with a higher than expected load the current will be higher than it is designed for. You probably need something with a higher rated power for a hacksaw unless you reduce the load by gearing or changing pulley sizes..
|Thread: What Did You Do Today (2017)|
Made a bush for a keyway broach. The bore is 52mm and the keyway is 6mm. I didn't make the wheel, it's too big for my lathe. The two slots are instead of a shim, one is 1.6mm deeper than the other. The holes and ten sides were machined at one setting to make it easy to align the keyway 18 degrees round from a tapped hole when the bush is put in the vice to cut the slots. The holes on the opposite face of the wheel are 36 degrees off from the visible face so the keyway is positioned centrally between tapped holes. The broach from Arceurotrade is my payment for doing the work.
|Thread: Yaskawa VFD|
Have checked the mcb and it is 32A. It does supply other things as well as the workshop.
I can't remember what size mcb I have in the supply line for my workshop but occasionally when I switch on one of the VFDs I have the mcb trips. It is only about 1% to 2% of the time and I usually switch it on before anything else apart from the lights so it is a slight annoyance only. It must be if I switch it on at the worst possible point in the ac cycle. Once on the mcb has never tripped in use.
|Thread: Something special coming in issue 253 of MEW|
At the moment I can't see anything in my future work that would require an automatic tool changer for my lathe. I can see the appeal for someone who wants to make 400 super special, identical hinge pins for a tracked scale model.
For the occasional use I can envision a simple tool changer that is manually moved to each position. All that would be required in the CNC code is a pause using M0 with a comment saying something like "change to 60° threading tool then press cycle start". I don't think my quick change tool post is quite up to the repeat accuracy required but that may not be the case with all of them. This is similar to the tailstock turret system where the required tool is rotated into position by hand as it is needed.
Regarding the pawl in the earlier picture I thought there was a possibility that there was dirt on it that looked like a crack. I also think it looks a little too slender for the loads that will be imposed on it and if not already cracked then it would probably happen at some point in the future.
|Thread: Discouraged Feeds on a Lathe?|
The Smart and Brown model M has a selector that feeds either the leadscrew or a keyed shaft for powered feeds or screwcutting. The leadscrew drive has a shear pin in it so that if it is overloaded you have to replace the shear pin and in theory you could carry on threading without losing your position in the thread. On the feed system for powered feeds there is a slipping clutch in the apron which will prevent overloading the drive system but would totally mess up screw cutting if a rapid feed rate was used to cut a thread. So in this case there is a definite difference in screw cutting compared to powered feed.
With CNC the difference between powered feed and screwcutting is only a matter of synchronization with the spindle position when threading.
|Thread: Bandsaw woes|
I have had problems with the guide rollers being too tight for the blade thickness. Over time the blade was squeezed enough to thin and stretch the part that went through the rollers. The blade did not stay straight as a result and the weld snapped with very little wear on the teeth. I opened the gap slightly on the guide rollers and now the current blade has been in a long time with no sign of the distortion to the blade that was showing up before. Industrial bandsaws often have some sort of indicator to let you know when the blade is at the correct tension. I have seen pressure gauges on some and on others a Belville spring system with a coloured ring on part of the tensioning mechanism. When it was tight enough the coloured ring was in line with a pointer. It is surprising how much tension is put on some of these blades.
Clarke CBS7MB I got for half price because it had been dropped in its crate.
|Thread: Alternative to PC based Cnc controllers|
The problem with all this is - it makes me want to spend some money and play with one myself. I look forward to reading the complete tale when it is written up.
PS Is play the correct word for this?
Edited By Martin Connelly on 11/04/2017 14:18:15
|Thread: Work Holding: drilling and taping a ball bearing|
How much of the surface of the ball is actually used? I ask this because it looks to me like you could just turn a spherical surface on the end of the rod to achieve the same result. Use a suitably hardenable steel and polish afterwards.
|Thread: Drilling holes|
The problem of taking too large a bite with a big drill is that the feed per rev for the outside edge of the drill is too large for the edge near the centre. If you reduce the feed per rev to suit the inside diameter then the outside runs the risk of rubbing instead of cutting. So a technical reason for going up in stages that is not just to save overloading a small machine.
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