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Member postings for Martin of Wick

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

Thread: Newton Tesla Motor units
17/03/2022 10:04:30

The quick answer is yes, there will be a relationship from which you can estimate the RPM.

But this will depend upon the type of VFD, (vectored or not), the various loaded parameters and likely only valid for no load or constant load conditions.

The other question is WTF do you need to know lathe RPM to any degree of accuracy?- it tells you nothing.

The approx speed is usually more than adequate if you don't want to fit a spindle counter.

This was achieved in my case by using a linear control pot and setting the min and max frequency of the VFD to give the desired min and max motor RPM in line with manual belt speeds at min and max pot positions (usually 1400 to 1500 for a 4 pole).

Then print out a 0 to 100 dial for your control pot, so the approx spindle speed can be determined by the dial percentage times the max speed at any particular belt setting, plus or minus say 10%. Therefor if your pot setting is 40% and the full speed would be 600 RPM at the given belt setting, then 40% of 600 would be about 240 +/- 20 or 30 RPM.

As a caution, I would not drive the motor for high load operations at any less than about 20% of full pot deflection. If you have a fancy vectored thrust unit, you may be able to go to lower frequencies without cooking your motor.

 

I would add, that my experience has been the lower the frequency, the larger the range of  speed variation under load. But then I am partial to the cheapest and nastiest VFDs money can buy, so your mileage may vary.

 

 

Edited By Martin of Wick on 17/03/2022 10:07:59

Edited By Martin of Wick on 17/03/2022 10:12:55

Thread: Spindle Play in Sieg SC4 Lathe
09/03/2022 15:46:33

Was Gonna say check all carriage, x slide, top slide, tool post gibs and fastenings before blaming the spindle.....

Thread: ML7 toolpost Thread
06/03/2022 18:47:38

If it is in its unmolested form it should be BSF - having 18 TPI, you can check with a rule.

Edited By Martin of Wick on 06/03/2022 18:47:56

Thread: Myford ML7 1956 ... Question on drive belt and Stalling when cutting
06/03/2022 18:17:13

1 With the belt de-coupled, does the spindle revolve freely when chuck spun by hand. If not, find out why before proceeding.

2 check for any obvious oil contamination and clean.

3 If you have, as I think, a link style belt, bear in mind the tension may often need to be much higher than for a normal A section V belt, and the cheaper the replica belt the higher the tension required, usually.

4 Replace dodgy belt with standard or segmented A section belt for little cost, or if you have to, get a genuine Fenner product replacement. You should then be good to go with 40 thou cuts (if you want to be brutal).

BTW a suitable basic 23 inch A section V belt should cost about a fiver plus delivery from any number of  bearing, drive, belt, motion  factors  on the net.

 

Edited By Martin of Wick on 06/03/2022 18:28:37

Thread: DRO Scales
25/01/2022 12:13:21

Without knowing exactly what scales you need, difficult to advise.

UK Vevor have a good deal on basic 5um glass scales for sino dro & clones at the moment. Ordered a 2 axis set on Sunday for WM16, delivered today! (usual disclaimers etc).

Thread: Slowing lathe RPM
10/01/2022 11:22:58

I generally start with this....

RPM = SFM x12 / d x 4 as a first estimate of starting point for lathe RPM ( in yards feet and inches).

So assuming turning a 2 inch billet of Al, something up to around 900 RPM would be OK based on 600 SFM, assuming the material is of a free cutting nature.

You can double that RPM with XXGT carbide type tools, but you have to bear in mind the size and power of the OPs lathe, 'cos you cant really go hoofing massive cuts on a Taig.

Thread: ML7 lathe bed
04/01/2022 10:12:39

As an unhelpful aside, while you are carrying out detailed and complete measurements of bed wear, I suggest you check other components, ie, various lead-screws and their nuts, cross and top slide for rocking and lifting, all the various oilite bearings including countershaft etc. etc...

Only sayin cos if the bed is badly worn, then everything else is usually well shagged also. Then your small project suddenly becomes a bottomless money pit as well (wonder how I found out?).

Secondly, if you are considering a second hand bed, you gotta ask the question why is it for sale? I would suggest it is extremely unlikely that you will find one in an unworn condition.

Edited By Martin of Wick on 04/01/2022 10:14:50

04/01/2022 09:25:36

An all to common problem, but don't assume the worst until you have carried out other checks and considered other mods. If you search the forum posts using terms such as myford, bed, regrind, worn etc, you may find something useful.

I had mine done at Slideway Services of Nuneaton in 2015 by an uber-grinding maestro (since changed hands so I don't know how receptive they will be to small works now). At that time it cost about £250 for lathe saddle (turcited for wide-guide) gibs and clamps on top of which was fuel for the 2 x 300 mile round trip to drop off and collect.

Expect regrinding to be someway north of £300 now even if you can find an outfit with sufficient equipment, expertise and interest to carry out the work now.

Thread: VFD - which is best please ?
01/01/2022 12:03:06

For the benefit of the OP, good advice at the beginning of the thread.

If not familiar with this class of device, almost any branded product from a reputable UK supplier will be suitable (several have been mentioned). You will have peace of mind, a guarantee of some sort and useful back up. one of the vendors supplies helpful quick set up diagrams if you go down the DIY route.

Avoid web sourced unbranded generic VFDs unless know what you are doing, content with the associated risks of inadequate documentation, zero back up, worthless guarantees and quality control issues. etc. Many (including myself) have managed to get useful service from these units but that has come (in my case) at the cost of a great deal of time and effort trying to understand and test the available control parameters etc.

Assuming you purchase from a UK supplier...

You will pay more (much more in some cases) for a full installation solution/package of motor pendant VFD all wired up, but it will save you time and may be a lower risk solution.

You do not need a complex VFD device with hundreds of weird and wonderful parameters that you are unlikely to use and that has a premium prices accordingly. A simpler unit will be perfectly adequate for a manual lathe drive, just check that the control functionality suits your requirements (ie do you need braking, ramp start, reverse, jogging, e-stop, reset etc). I assume that your lathe is not set up as a CNC device, in which case you may need additional control functions.

A vectored thrust device to give more low speed torque is desirable but you are likely to have to pay more than for a simpler device.

The VFD power rating should match the rating of the intended motor. A slightly higher rated VFD will be OK, but not a unit that is rated at less than the nominal motor power rating.

Ultimately I would ask do you really, really need a VFD? If the answer is because you want to use a 3 phase motor and benefit from the smooth and quiet power delivery and low voltage controls, then pass GO and expend £200 in blood and treasure.

If the answer is 'because I cant be arsed to change belt position every time I switch from turning to threading' then you might well be disappointed with the outcome.

 

Edited By Martin of Wick on 01/01/2022 12:15:45

Thread: Myford super7 saddle / tight toward tailstock
19/12/2021 20:18:42

Can't honestly remember what the gib looked like on my S7, I dont recall any threaded holes in it though.

Wear will occur on the sides of the shears, but also on the top and bottom. Don't tighten the saddle gib for this test, Set it sufficiently loose to all full and free saddle movement up and down the bed.

Then check to ensure the saddle clamp plates are in place and all bolts are all fully tightened (just in case, cos I am prone to finger tightening then forgetting to nip up fully!). When fully tightened, these should not significantly affect movement in the Y axix (or the X!)

Can you still move the saddle nice and easily up and down the full length of the bed -

Yes? great, now move the saddle so its LH side is at the location you measured the greatest lateral wear on the shears. Then seize the front of the saddle in both hands, one each side, fingers on the plates, thumbs on top of the saddle but also contacting the bed and attempt to lift and or rock the saddle vertically up and down to detect any looseness in this location. You are only concerned with detecting vertical movement in this test. If there is no vertical movement that you can detect you can try the same test with a DTI.

If there is still no, or virtually no movement up and down, then consider yourself more fortunate than most as there is insignificant wear to top and bottom of the shears.

Edited By Martin of Wick on 19/12/2021 20:21:53

19/12/2021 14:26:58

Ordinary MS will be fine, gauge plate OK, no need to harden. Probably best to avoid the copper based alloys. I have even read of someone that claimed to have used some of the blue steel banding strip from large packing cases!

I had (still have) a 1947 ML7 that had much worse wear issues. In the end I had to admit defeat and used Slideway Services to regrind. I asked them also to grind out the saddle to allow a wide guide conversion using turcite. They did a superb job but the proprietor cautioned me that the turcite must be kept fully lubricated at all times to avoid rapid wear, that could in theory impact the angle of the saddle over time.

One thing you could usefully do is check play in Z axis of saddle at the unworn part of the bed and again in the wear zone. Set Y gib to give smooth play free movement over the bed. Set the saddle retainer strips to give you nil/minimum vertical play at the RH end of the bed (shimming/de shimming as required. Move saddle to wear zone and check vertical play again. If acceptable to you, then you are good to go. I could probably tolerate a thou or so movement.

17/12/2021 10:43:05

Couldn't say for sure.

In theory it should, assuming your early model has the 3/4 inch leadscrew (my opinions not to be trusted on early S7s as you have discovered!). I have a late PXF version of the S7 and the saddle looks quite different (although the fitting dimensions to the bed must be the same, albeit with the middle bearing surface cut back for clearance).

Not quite sure what you would gain unless the current saddle is in poor condition, (or you don't have access to a mill or second lathe to trim back inner bearing surface, which is usually the problem for most of us!).

Perhaps somebody can chip in if they have gone down the saddle replacement route?

I would suggest that you acquire a micrometer(s) a piece of paper and a pencil and take some defined and detailed measurements of shear width and depth over the bed ( tablet and spreadsheet will do if you are a young whipper-snapper). This will accurately map the location and amount of wear and give you a good idea if the wide guide fix will work. You could also measure the gap between the back of the rear shear and rear saddle bearing surface with the saddle set up in the usual arrangement towards the back of the lathe. Feeler gauges may help here.

You may then be able to find / fabricate a suitable piece of steel to that thickness plus about 0.020 thou and epoxy it to the saddle back bearing surface. This will pull the middle bearing surface away from the front shear enough to avoid binding. This particular kludge depends on there being enough slop, flop and fitting clearance on the apron fitting and leadscrew clasps. clearly if you go too thick on the stick on plate, you may lose leadscrew/clasp nut clearance. This method avoids having to cut back the middle bearing on the saddle.

Disclaimer - I have only read about those claiming to use this approach second hand, so cant guarantee success.

16/12/2021 21:36:49

Sorry you are quite right, if it says S7 then it is. The early S7 apparently had the same poor saddle design as the ML7. Change to the rear shear bearing on the S7 was only implemented in 1972 (I thought it was earlier for some reason, but just checked on lathes.co).

16/12/2021 21:14:12

BTW the saddle design suggests your lathe is an ML7 not a Super7

16/12/2021 20:36:45

Don't think you have missed anything, the shears are worn at the headstock end, most of the wear will be on the front shear. The narrow guide myford is a poor design which is why the later models  use the outer edges of bed shears as the saddle bearing surfaces.

The front shear is mainly used on the narrow guide design and this is subject to most of the wear, not helped by the short bearing surface of the middle of the saddle which allows the saddle to rock. As most of the work is usually done close to the headstock, the front shear inner and outer edges wear most in that area over time. This is confirmed by your visual -Scraping marks are present on the inner edge of the front way from the tailstock to midway along toward the headstock, and then fade

Unfortunately, your lathe exhibits the most common problem with that class of machine. Not a lot of wear visually observed is more than enough to cause this problem. Effectively your front shear tapers down towards the headstock.

If you cant live with the problem and adjust the saddle fit to suit the job you are doing, then you options are

  • You can get the bed and saddle reground if you can find anyone still capable of doing it and you have deep pockets
  • You can do the standard documented wide guide modification which uses the outside of the back shear
  • Some people have claimed that they have scaped/filed/ground the shear edges, but I wouldn't recommend it

Should also add, that if the bed is significantly worn, the shears can also be thinned on the z axis towards the chuck, so you will need to check the thickness of  front and back of each shear chuck to tail every 30mm along the bed. If this is the case, the wide guide mod may not solve the problem.

 

 

Edited By Martin of Wick on 16/12/2021 20:40:47

Edited By Martin of Wick on 16/12/2021 20:48:09

Edited By Martin of Wick on 16/12/2021 20:56:24

Thread: Another chinese lathe rises through the smoke
16/11/2021 20:38:53

Hmm... yes accepted, there are brands and brands and Seig is probably upper quartile. Indeed, the article makes the point that some suppliers play a bit of a game with the numbers.

Most of what I end up with is very much from the other end of the quality spectrum to bottom of barrel stuff, so I have reasons to be cautious!

Thread: Heat resistance of PLA
16/11/2021 20:12:39

As stated, heat treating PLA (referred to colloquially as 'annealing' will both:

  1. significantly strengthen the PLA part
  2. make it temperature stable up to about 120c (ie as good as ABS)

But it needs to be done relatively carefully to avoid warping or distorting the part. I use one of the small consumer bench top ovens that I removed the top element from. I also recalibrated the temp control using a temperature probe on the middle shelf (ie where the item to be heat treated is placed) to have a more accurate indication of actual part temperature.

The best results I found are obtained by bringing the part up to to 60c, 80c, then 100c in one hour for each stage, and then back down in one hour stages. There can be very slight shrinkage on X and Y axis that may affect larger parts.

I would like to be able to rig up some sort of programmed PID control to do avoid having to do the settings manually but haven't been able to figure it out!

If you go down the same route, try to get a circulating oven if they make them - the internal temperature will be much more even.

Thread: Another chinese lathe rises through the smoke
16/11/2021 19:50:25

Your DC motor was rated at 500W input power, as in volts times amps your 350W induction is shaft power, an entirely different thing.

Is it true all induction motors are really rated on their output power? If so then I have learned something new.

I say this because I have come across ancient* 1/4 hp motors that subjectively appear to be able to deliver as much turning force as some modern 1/2 hp motors (although I have never been able to precisely measure this to confirm). I did query once with a motor man who reckoned that older motors tended to be quite significantly under-rated on the plate with respect to expected duty, to ensure operational reliability.

What I do know from experience is that Chinese ratings appear to be for the absolute, full blown, maximum power dissipation the item will tolerate at the point of magic smoke release. Numbers are based on marketing rather than considering any actual duty. For reasonable operating, I usually assume 50% of stated values as indicative/safe power.

*ancient defined as circa 60 to 70 years old

14/11/2021 20:12:55

I would go for half a horse min. I have a 350W induction motor on an equivalent lathe and it certainly doesn't feel over-powered. However it does feel substantially more powerful than the DC motor it replaced (that bogusly claimed 550W!).

If I didn't also have the 1HP Myford, I would probably up the drive unit to 500W.

Edited By Martin of Wick on 14/11/2021 20:37:41

14/11/2021 20:02:07

For those with the cash, the NT solution will be simple, robust, safe and least faff.

If 'twere me, I would find a new 3 phase 350W or 500W motor circa £80 to £100 and a generic 750W VFD circa £50 to £70. A s/h motor would be OK, but you may have to search about to find the right one and they never seem that much cheaper than new.

If you do not feel completely confident/competent to wire up such power devices and make a simple control box to suit your purpose, I advise you to take the NT route.

Depending on motor speed selected, (ie. 2 or 4 pole) you may need to adjust the drive pully arrangements to suit your requirement.

PS -  avoid open frame motors if possible, sure they run cooler but they have a propensity to ingest swarf unless well protected

Edited By Martin of Wick on 14/11/2021 20:06:57

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