Member postings for Ajohnw

I can explain the principle these work which might help.

If there is a rupture type emergency stop switch the mains goes in through that. Rupture as the force on the button is sent straight to the contacts so they may open even if slightly welded.

The general idea is that the whole lot defaults to off if the power fails so the on button energises the really coil and contacts on the relay latch the coil on. The stop switch is in the relay latch circuit to that when it's pushed it deactivates the relay. The machine is powered via other relay contacts. It should provide both live and neutral to the machine via the relay

2 arrangement are shown here less powering the machine but check what I have just said in case there is an error. Doesn't look like there is

**LINK**.

John

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Mine is by Draper. Not sure but this is likely to be after they bought Mit and tried to sell expensive under their own name. It even states made in Japan on it. I did have a finger DTI and holder etc later that was definitely from that period. The adjustment on this one is a little on the coarse side for a 1/10,000 dti really but not that bad. I recently bought the dti that is on it. My previous one was showing signs of plunger wear - the readings drift in a direction according to the way things are rotated. I generally use the tip of dti's to gauge by eye before actually engaging the plunger. The long travel is there for mishaps really.

The spring on the finger dti stand is a better arrangement in some ways. It's very hefty and at the bottom of the main stem and has a limited range of adjustment. The "spring".can only compress by about 1.5mm Not sure how Mit adjust the one I linked to. The price isn't too bad for their equipment.

John

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The 2nd one from top left has a fine adjustment but they don't really say how it works or the travel.

**LINK**

John

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I use the spring adjustment nearly every time I use it but then as I have had it for a long time I'm used to it. I generally set the plates the spring presses on parallel or leave where they happen to be.

If I'm not using that I use this currently with the long finger fitted. I can also use it on the other stand.

The tin is full of boxford change wheels and my favourite stone for tools and a larger one intended for sharpening microtome blades I am playing with sits on top. The smaller stone is back to it's old self now I have used a diamond lap to remove the HSS clogging it up. It's improved the microtome one too but that one is insanely fine.

Forgot to mention the bar just above the magnet on the finger DTI stand is also a spring but I have lost the screw that adjusts it some how. Need to make another. The joints are ball joints. Easy arrangement to make if some has a ball turning gizmo. The plates each side of the balls just have depressions in them.

John

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Edited By John W1 on 16/06/2015 00:06:01

I just make sure there is some tension in the spring Neil. Rotating the bar with the spring on to where it needs to be does exercise the grey matter. I have seen no reason to change mine at all. They sold well and I have seen them in several work places.

The only catch I see is that it can be hard to know which way the spring will be bent when the DTI gets where intended so some tension in the spring is needed - bends the arm and reduces the reach but that has never caused me any problems.

John

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They are available from a more reputable source, generally beyond reproach

**LINK**

Same one as on ebay? Pass. Sometimes the same thing is made to a better standard. Sometimes not.

John

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I've been using one like this for years usually with a 1/10,000 dti on it.

http://www.ebay.co.uk/itm/Heavy-Duty-Dial-Test-Indicator-Magnetic-Base-DTI-Stand-For-Dial-Gauges-NEW-UK-/181445575807?pt=LH_DefaultDomain_3&hash=item2a3effc47f

Bought from Alpine House who some may remember. The arm adjustment is rather useful. I also use a small magnetic base with a finger type DTI on the end. Usually the machine slides can be used to position that. The other stand is handy when that is not possible. I assume these are the same products as when I bought one and also in real terms cheaper. It was a rather new idea then and actually pretty expensive compared with others they sold.

John

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IIf you want to save money make sure that the lathe comes with plenty of equipment and if possible try before you buy or at least arrange a decent demonstration. Same with the milling machine really and for full capability a combined horizontal and vertical machine is a better idea really. With this type the vertical and horizontal heads are attachments. They are about but it's best to find one with both heads.

On lathes Myfords can be excellent if correctly adjusted but the general arrangement they use isn't really conducive to still working well when there is wear especially on the bed. or poor adjustment. It's no mistake that the vast majority of lathes use prismatic beds and have done so for a long time now. The reason is simple really. If designed correctly cutting forces force the saddle against the bed and as things wear they still tend to remain in contact. Things don't work out that well on Myfords. The Raglans use the same style but as the bed is wider they can be a lot better. The other aspect is the guide length. There is a principle usually referred to as narrow guide. The idea is simple, say you have a bar in hole with 0.0005in clearance. If the hole is 1 diameter long the bar can waggle by so many degrees, think what happens when it's 10 diameters long. It waggles a lot less. Prismatic beds can have very high ratio's especially if the tail stock runs on another one. Often that rail is used to locate the headstock which means that the ends of the saddle can pass both the tailstock and the headstock making them even longer. The tailstock rail is unlikely to wear much as well maintaining alignment. The same can be done with dovetail beds by running then tailstock in a "slot" in the centre of the bed. Myford have done that in the past but seemed to stop doing it. Probably to reduce the weight of lathes like the ML10. The 7's work like this but the guide is a lot wider than a prism and going on Raglans the bed is too narrow but Raglans have a similar problem.

If I'm not careful I would start on headstock designs but length comes into that as well for similar reason but related to the accuracy of the positioning of holes for bearings. Plain bearing correctly adjusted and in perfect condition can result in a better finish than can easily be obtained with races. Races have the advantage that they can be changed and are usually pre loaded and offer low friction. The same can't be said about the Super 7's front cone. A common complaint is that they wont drill as hole as big as the ML7. Some of that will be down to adjustment, not easy and temperature changes. The ML7's problem is at some point the need for new bearings. These are hand scraped to fit the spindle but I understand some have managed to cast white metal ones in place easing the scraping work. It must be fun to align the spindle first. Scraping would have to be used to fix any problems in that area is it is with phos bronze which Myford offered near the end.

This sort of explains why I switched to a Boxford but they are heavier lathes than the 7's and most are under drive. The other reason was all of the tools that came with it. I'm not saying don't buy a Myford or a Bridgeport. There can be excellent examples of both about also crap Boxfords but they do react better to general wear and tear just down to the design of the bed. They and similar machines used to be popular with people who made a living as home turners, batch work for various companies. Some Myfords have probably been used for this sort of thing as well. It's surprising how quickly lathes can wear when used daily for long periods. My idea of a lathe is one that produces perfectly parallel work with a lovely glossy finish. I have used lathes like that but have to be more realistic at home.

John

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I wonder if this is a case of all will give a wonderful finish if emery cloth etc is used on it? I assumed a good straight turned finish is required. Just about anything can be polished up.

John

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Edited By John W1 on 15/06/2015 09:15:32

Edited By John W1 on 15/06/2015 09:16:15

These are not bad lathes Hobbymat Alan so I feel it is worth sorting out especially if it's just the handle fitting. These lathes are even fairly precise. I found 2 problems, one I mentioned was found by the owner after me - the original tool post casting on the later Hobbymat are a bit weak. The other was prolonged screw cutting. The dog clutch on the end of the lead screw needed some attention. I feel it needs a more robust material but at the time my best source of cheap accurate 1MT arbours was either HSS reamers or drills so it was working fairly hard. The fix was to just run a file over the mating parts.

John

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I wondered about that Neil, melts at around 750C and boils of at circa 1500 from the wiki. Sounds feasible but silver solder usually melts well below that and a gas air torch can put too much heat in so I wonder about the 1500. I'd guess it needs to be hotter than 750 to do it's job.

John

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I'd guess that carbide of some sort will be the cheapest option for that many holes. I hate the stuff. Last time I did anything with it not able to use optimum conditions one hole drilled fine - same drill didn't on the next. That then took 2 drills to complete the job as the 1st one had done the damage. So as I see it if this happens you will ideally need carbide anyway.

The drills came from a toolmaker who was only allowed to use them for one hole in an exotic hardening material as any problems were too expensive. Wish I still knew him. They were still sharp. Very sharp high quality drills.

I don't think I would be too concerned about using carbide at the right speed in a hand arrangement for chamfering but that's just a gut feeling.

John

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I have an interest in home casting of late and have been watching video's by Myfordboy - good source and an excellent design for a rolling machine. In one of them he silver solders - reminded me of brazing and lead burning at times, same sort of technique. Soft soldering with a torch needs the same technique. Thin metal isn't so bad as it will heat up quickly and hopefully before the flux has burnt off.

John

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Torch soldering / brazing etc can be a bit counter intuitive. What I think you will find you have done is put the torch too close to the work. The flame is more than hot enough to boil the flux off before the work has heated to the correct temperature. The answer is to move the torch back away from the work and heat things up more slowly. You could look around the web for flame temperatures but it would be better to find out for yourself on a couple of suitably sized pieces of metal. Find the distance that causes the flux to melt is a good starting point. You will probably then have to go closer once the work has reached that temperature to get the silver solder to melt but not so close that flux boils off. Done this way it will take longer to heat the work - that's the catch. People are inclined to heat it up as rapidly as possible and might even put the end of the blue cone on the work.

I've more experience of gas air brazing but exactly the same factors can apply.

John

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303 is fine. You might find that as with all extruded materials that the skin is a bit dodgy but not much needs turning off to fix that.

There are better grades. If you google StainlessSteelsforMachining_9011_.pdf you should find a run down of many different types by the Nickel Institute

I just looked and it is still about.

John

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Jam nuts usually have the same thickness so that the same number of threads take both forwards and backwards thrusts. That should help maintain equal wear.

Where handle play is adjustable it's usually some sort of threaded bush some where and some means of locking it in place. I say somewhere as I have a feeling I have seen it in the actual handle on a lathe.

John

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I'm old fashioned. If a tapped hole matters I go 1/3 of a turn in, around the same out to break off the cut and so on. I understand that the usual straight flute tap is designed to be used like that. I don't use a protractor to measure the angle turned and would guess it might be less than 1/3, just what's comfortable. I also make an effort to ensure the tap is aligned with the work and to keep it like that - going in at an angle is a certain way of breaking smaller taps or having them jam up, Too much of a turn will break very slender taps as well.

John

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There will be back lash so the aim is to work around it using the dials. Say 2mm of outward movement is needed. The tool is wound out 2mm plus backlash and plus some more and then wound back in to the correct reading. Then if there is a need to move the tool in further back lash has already been taken out.

Things are the opposite way round when boring.

0.3mm is nothing and you may find that adjustments just close up the nut and as there will still be some play you might finish up bottoming one thread with another - not a good idea. 0.3mm might concern me on a slide that used a 1mm pitch lead screw as it represents 30% play but that wouldn't make the lathe unusable, just indicate significant wear or a poorly produced item.

There is an arrangement usually called jam nuts - 2 nuts and their spacing can be adjusted. Rare and not of much use really as some play is needed for lubrication.

One aspect that is worth looking at closely is if part of the play is actually down to the handle / dial moving backwards and forwards. This is adjustable on some lathes but I have seen it "built into" some Chinese lathes.

John

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Edited By John W1 on 13/06/2015 15:21:52

Those serial taps sound like they might be a good idea - reduce back cutting.

With M5 causing problems though I wonder about the tapped depth. There is little gain and then a fall off in strength as thread engagements increases. Even with precision fixing screws it's pretty common TDO practice to limit the engagement length to 1 to 2 diameters of the thread. Some reckon less than 2.

John

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The metric tapping drill being diameter - pitch is fine but if you look at charts that give full thread data I think you will find that this will mean cutting part of the radii that is specified for the root and doesn't really account for any tolerance on the tap itself or the drill. I never have any problems with free cutting stainless but the real thing is a lot more difficult and having 1st and 2nd taps becomes more important. The free cutting one is slightly magnetic. I always check as sometime when buying small pieces the suppliers might pick the wrong type up.

To be sure of clearing rads and drills being slightly undersized etc 4.4mm should do it or even 4.3 really but if you only have a plug tap you might still struggle. Scraping a bit of hand bar soap onto taps makes a fairly decent lubricant.

I did have problems with one small piece I made. M4. Turned out that the die was well under sized. Initially I couldn't understand what was going on. It's might be worth checking the diameter of the taps you are using.

John

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