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Member postings for gerry madden

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

Thread: Dial indicator probe threads
16/03/2019 19:41:49

Thanks Michael and Chris very much for your inputs. When I read Chris's reference to 'metric dies' I suddenly remembered I have a box of small ones somewhere! Just found them and the 2.5 seems to fit 'acceptably' so just about to try with this.

16/03/2019 19:08:15

Does anyone happen to know if there is a standard thread for dial indicators probes ? I need to make some extension bars.

Thread: Plastic Balls in Bearings?
24/02/2019 13:26:41

Ceramic balls can be white or grey. But they are very light so could easily be mistaken for a plastic. I know that dyson has done some fantastic things with motor technology and he outstrips the traditional Japanese designs with speeds in the region of 100,000RPM. So he may well have determined that the benefits of light ceramic balls in terms of friction and being less demanding of lubrication are worth the extra cost.

Of course the 'plastic balls' may have been in a 'cheap n nasty' in the "turbo" head or something else less glamourous.

Thread: Mill tooling runouts
23/02/2019 15:44:58

Ive started to strip my mill and inspect the parts to see if I can improve the rigidity. The head is off the vertical slide and the spindle is out of the head.

The first thing to become obvious was that the clamping face that goes against the slide was far from flat !!!

dscn6595.jpg

When I put the casting on a flat surface and it rocks right and left. The finish of the face suggests its been on a linisher instead of being ground ! Extraordinary! Witness marking on the face confirms erratic and one-sided contact with the slide.

Whether it has always out of flat or has warped over the ten years or so that I've had the mill it I'm not sure. But I suspect the former based on the dreadful linished finish.

So the first thing I need to do is get it face ground. Does anyone know of a good place to go in the Leighton Buzzard / Milton Keynes area please ?

The quill is a clearance fit in the cast head of course and is clamped on the lower edge only. Clearly this doesnt help with stabilising the upper portion of the quill due to the 'cut' not being completely through the body. So Im thinking of completing the cut and fitting another clamp bolt at the upper position. I'll have to move a screw hole of course but any thoughts on the wisdom of this modification ? I can think of a few risks which might or might not be manageable but I welcome your thoughts on whether I should be so drastic.

dscn6596.jpg

Inspection of the spindle threw up some surprises too. It spun smoothly with a nice uniform 'hiss' typical of well preloaded-bearings. I put it on some V-blocks and tried to measure the runout. After the struggle of getting the DI into the internal taper I could confirm this to be around 2 microns.

dscn6590.jpg

I did initially try measuring the spindle runout on a chuck inserted into the spindle. This produced variable results of up to 7 microns. Playing about I found the cause of the variability was micro-movements of the chucks taper in the spindle. Small differences in taper angles and other geometric non-uniformities was allowing the male part to rock. I hadn't used the drawbar to pull in the chuck and that might have helped reduce the rock. I'm pretty sure though it wouldn't have eliminated it completely. Clearly there are MT2 tapers and there are precision MT2 tapers !

Another interesting and unexpected characteristic of the spindle was that applying a few Kgfs of load to its nose caused not only elastic deflections but some semi-permanent deflections too. The latter were in the order of too 3~4 microns which was a bit concerning at first. I then found that with the tiniest rotation the spindle returned exactly to its origin. Clearly there is frictional hysteresis in non-rotating ball bearings too. I have spent years in bearings and didn't know that !

12/02/2019 09:56:21

12/02/2019 09:55:05

….no it wont allow me to paste the graph or even a snip of the graph..

12/02/2019 09:52:36

Hi All,

I have now made some more detailed investigations into the rigidity of my mill. Measuring deflections at the chuck with loads up to 15Kgf I find the compliance in the right and left direction (X axis) is twice as much as that in the Y axis.

Graph in next post - it doesn't like it inserted here for some reason!

Its surprisingly linear too.

There was also some hysteresis, in other words after applying and releasing the loads the spindle didn't return to exactly the same place. The 'free play' if I can call it that (but its not a noticable rattle) could be minimised by excessive tightening of all the gib screws and headstock clamp bolts but never completely eliminated. So I think some is in the spindle itself. The minimum I could get was about +/- 2um. Without normal gib settings it was about +/-6um.

As mentioned in my previous mail, when I put the DI on the spindle headstock, the deflections were of a very similar order which suggests that the elasticity is in the structure rather than in the spindle itself. The headstock looks quite rigid so I'm wondering if there is some 'rock' / weakness in the joint between the headstock and the vertical column. I'll begin taking it all apart to see if I can find anything that could be easily improved.

Thread: Testing for isolation
02/02/2019 15:07:33

I have always wondered why we feel anything at all if we are isolated from earth and touch a live wire with one finger only ? Is it a capacitance effect allowing a tiny current to flow momentarily till we are raised to the live potential ?

Birds land on HT cables and clearly don't even get a tingle of they probably wouldn't do it.

Any thoughts ?

Thread: Guidance on selling my late fathers machinery
28/01/2019 20:16:37

Hi Oliver, PM sent.

Thread: Lathe levelling
23/01/2019 15:20:30

This topic has deviatingly reared its ugly head in another thread. Rather than perpetuate the error I thought I'd start a new one.

My lathe sits on a metal cabinet on top of a carpet It wasn't "level" on first installation so I fixed it down solidly on large 4mm thick washers at three points. Under the forth foot (tailstock front) I inserted a wedging device along with the pull-down bolt.

Now when I want to do some precision parallel turning, I do a quick machining of my test piece. If there is a difference in diameter between the two ends I simply slacken the bolt on the adjustable foot and pull out or tap in the wedge a fraction. I then tighten the bolt and make a final check.

Its so simple and I often wonder why no one else (or manufacturer) does something similar ?

Thread: ARC's Adventures in China 2019
21/01/2019 15:40:36

Several references to 'vacuum' here. Surely its just an standard precision machining industry air-gauging system for measuring a fine (micron) toleranced feature ?

Thread: Mill tooling runouts
31/12/2018 13:56:25

They say the devil makes work for idle hands so during a spare afternoon last week (I had intended to tidy the workshop!) I thought I would do some runout checks on my mill tooling. I seem to have acquired a Jacobs, Rohm and ER collet chucks over the years so I thought I'd see how they compared. For each check, I assembled the chuck into the spindle, fitted the bit, measured and repeated this 5 times. The runout was measured radially on a smooth part of the shank of a 6mm bit approx. 5mm down from the jaws.

After averaging al the data this is what I found:

Jacobs 13mm

1)tightening by one hole 26um

2)tightening by 3 holes 25um

Rohm 0~6mm

19um

ER25 standard collet chuck:

1) normal tightening 12um

2) very tight 14um

What I didn't do is measure the runout of the spindle itself. But I did put the DI on the tapered bore of the collet chuck and this gave ne about 10um which suggests that the standard collets are not so bad.

What did concern me though was the flexibility of the structure. Just a light finger pressure on the bit, OR the chuck, OR the head, produced almost the same level of sidewards elastic deflection in the order of 15um. I definitely want to investigate the root of this and see if it can be easily improved.

Does anyone know what would be a typical 'spindle' rigidity value (um/N) in a small hobby mill ? Clearly though my problem is not the spindle. I think I have a problem with the stability of the clamping surfaces in the structural parts. When I know more I'll let you know.

Thread: Insulation tester - some guidance please
19/12/2018 18:08:09

Thanks all for your useful and thought provoking comments.

I suppose when I think about it, it wouldn't be the most frequently used tool in my armoury. But I occasionally do small mods to my domestic arrangements and it would nice to be able to say I have made 'that final check and all is ok'.

Also what seems to be popular at the moment here is two washing dryers tripping the ELCBs due to leaky heater elements. When I check these for insulation resistance with a normal Ohmmeter you seem to be able to get any figure you want up to 20Meg depending on the time of day. I was hoping that a higher test voltage would make this kind of check more reliable. (I do hate to spend money on parts when I don't have conclusive proof that they are defective.... of course its always ok to spend on tooling )

Thanks StephenS for your positive comments on the Mastech. That looks like a reasonable device.

18/12/2018 18:35:34

Hi all you competent electricians. I'm thinking of buying an insulation tester for Xmas and see that prices vary from around £50 to £500. (...there's even one for £13 which wont make the shortlist for that reason alone !) I don't want frills and already have an AVO. So is going for the lower end of the range sensible or is there something important that that I should be aware of when buying one of these devices ?

Gerry

Thread: loctite fixing
14/10/2018 16:24:20

Well the Loctite 243 was a disaster too. I then dashed out to the shops with 10 minutes to spare and got some superglue as per your recommendations, tried it and guess what... it works a dream. Thanks all for your instant help !

14/10/2018 14:52:32

Hi all, I'm just after a bit of guidance on workholding using glues. I wanted to mill some small aluminium parts today and thought I would try the technique of bonding them to a aluminium baseplate which would be more easily fixed to the mill table. The parts are 12mm wide, 10 high and 32 long.The contacting surfaces we very clean before glueing. I used a 'retainer' on the 32x12 face and left it for an hour. I couldn't pull it off with my fingers but as soon as I started to mill it detached. I kept my cut very very light. Now I'm about to try a medium strength Loctite, 243.

Is the face area just too small or am I using the wrong glue ? These simple techniques never go wrong in the 'Clickspring' videos !

Thread: kitchen fan speed control
01/08/2018 22:34:20

Hi Martin and Journeyman, thanks for your comments. I had a look at the website - thanks for the link - and it seems to suggest that this motor is an asynchronous design. And somewhere else I think I saw a statement that said something along the lines that 'all our motors are designed to be controllable'. Certainly from 1000 all the way to 2530 it behaves well which makes me think its the cheap controller that not good for slow speeds.

I would still be interested to know if the 260V output is realistic and the capacitor mounting if any one else has any thoughts ?

Gerry

29/07/2018 16:20:47

Hi All, I'm in the process of building hopefully a quiet kitchen extractor fan. After completing the basic structure yesterday I ran a few tests. At high speed most of the noise is aero so I need to work on this. But when I try to run at very slow speed I get a lot of electro/mechanical noise. The problem appears to be when the motor voltage is between 20 and 65V. Initially this will kick the rotor into gentle motion but this isn't maintained and it will slowly come to rest again. At the same time there is a strong mains hum which modulates with each turn of the rotor.

Interestingly if I flick the power on and off a few times without adjusting the controller setting, occasionally it will stop humming and start accelerating to around 1000 RPM.

I would like to be able to run quietly at speeds less than 1000RPM. So what may be wrong ? Is it the small 1A speed controller is not compatible ? Do I need a better one, or even a better motor ?

Another thing is the 2uF/450V capacitor - it has a big M8 stud for mounting which 'seems' to be electrically isolated from the usual connections. Do I need to use this stud or can I mount the capacitor in a plastic tool-clip instead ?

And finally, I have noticed that on full power, the controller puts out 260V into the motor. This is above mains! So is this normal or some kind of measuring error ?

fan on test.jpg

motor details.jpg

1a controller.jpg

cap 2uf 450v.jpg

Thread: Ball bearing axleboxes
03/03/2018 20:32:42

The picture wasn't so clear in the earlier post. So here it is again. A little better I think.

Regarding grease, yes there will be a little more friction than with oil but it will still be small compared with your seals. And once the grease in the bearings has 'channeled' (might take a few thousand rotations) the friction will drop to a level much closer to that of oil anyway.

hoffman axlebox.jpg

03/03/2018 20:01:43

Yes two ball bearings side by side will be absolutely fine in your case. Its sensible to put a small spacer between the inners. Just be careful that you don't nip the outers when you secure them axially. I wouldn't bother with oil though. Use ball bearings with a single metal shield and position the shields on the outsides.

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