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Member postings for AJAX

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

Thread: Help to value a Schaublin lathe.
02/03/2021 20:17:03

No screw cutting or power feed.

Mixture of drive pulleys including those for flat belt.

No back gear.

I'd estimate about £120 - £180

Thread: Sandblasting / gritblasting tools & machinery
18/02/2021 16:50:04

For removing flaky paint I find air driven needle guns are excellent if a little noisy.

Martin

Agreed - very noisy but effective. It might be worth noting a small compressor will not keep up and the needles will mark softer metals.

Thread: Chinese AT vfd heatsink and grounding
17/02/2021 15:34:10
Posted by John Haine on 17/02/2021 14:33:32:

The 52v could just be capacitively coupled to a floating heatsink. If it was really unsafe it would be much higher I suspect. The key question is whether you can safely earth reference the control input. Quite a few DC motor speed controllers are designed just for control potentiometers and need an isolator to use with a CNC system for example.

Understood, but that doesn't resolve the problem of an exposed metal heatsink that is in close proximity to mains voltages with no apparent regards to safety. Clearance between the incoming live and heatsink is minimal with no attempt at insulation.

17/02/2021 12:56:05
Posted by Dave Halford on 17/02/2021 12:00:57:

Good choice on the drill, i've been happy with my QDM750.

Shouldn't the VFD be mounted in it's own enclosure? When you go buying commercial components rather than retail finished products makers expect a different level of competence from the installer.

Typing too slow for Andrew sad

Edited By Dave Halford on 17/02/2021 12:01:39

Yes, I agree it should be mounted in an enclosure. But what happens when the VFD is mounted in an earthed metal enclosure? The heatsink currently floating above 50VAC would then be shorted to ground. Or how about an internal fault which brings the (unearthed) heatsink to mains potential? Seems dodgy to me.

The seller offered an 80% refund. I replied and said I'm expecting a full refund.

16/02/2021 23:28:47
Posted by Pete. on 16/02/2021 23:13:33:

Did you buy the one on ebay down on the south coast somewhere? There was two, that one and one from a dealer in Birmingham, I bought the one from a dealer as the other didn't have a post option when I bought it, first impressions are really good, there's no noticeable movement in the quill when extended to about 130mm, which is pretty impressive.

Well it's good there's another qdm750 owner on here, I hope you get a safer vfd, your life is worth more than an extra 50 quid.

No, I didn't buy the one you are thinking of.

Yes, I agree with your comment about safety. I will be reporting this one.

16/02/2021 23:26:57

Just tested the heatsink. 52VAC with respect to mains PE (ground). Not happy with this.

16/02/2021 23:02:09

Well that's a coincidence! I'm wiring up a qdm 750 right now.

£50 for the VFD

16/02/2021 22:40:20

I guess more than a few of you have purchased cheap imported VFD units. I bought one last week but now I'm looking at wiring it up I have had a closer look. No protective screen behind the PCB and heatsink, and the heatsink is not connected to ground. If there is a short to the heatsink it could be lethal.

Thread: Boxford AUD head refurbish
15/02/2021 00:06:03
headstock
Thread: 3D Printed CNC soft jaws for work holding
03/02/2021 20:04:06
Posted by DrDave on 03/02/2021 12:29:19:

That looks to be a really useful method of holding delicate work: why didn’t I think of it? A 3D printer is rapidly moving from my “desirement” phase to my “must have” phase.

Thanks for sharing this.

I didn't rate 3d printers much until I recently tried printing change gears for my lathe. They are excellent!

Thread: vfd inverter for Myford
03/02/2021 00:29:18
Posted by Andrew Tinsley on 20/11/2020 23:06:49:

If you are unsure of VFDs then don't buy a cheap Ebay Chinese VFD. They do work but need some experience to decipher the very poor documentation

Take Old Mart's advice and get a VFD from Inverter Drive Supermarket. Phone them up and ask for a recommendation.

I buy secondhand Siemens 420/440 or Alytivar VFDs , These are good quality units with excellent documentation and cost only a few pounds more than the Chinese VFDs I have installed 5 units so far with no problems.

Andrew.

Andrew, do you suffer any nuisance tripping with the Siemens VFDs? I considered getting one but the documentation states to avoid nuisance tripping an RCD must be type-B 300 mA. The RCD serving my garage is only 30 mA and I do get occasional nuisance tripping with a Eurotherm VFD.

Thread: Repairing stripped thread in Walker Turner bandsaw
28/01/2021 00:59:24

As mentioned earlier, I decided to go for the simple and secure option with a turned "shaft" mounted in the central hole and then cross drilled and tapped. I won't bore you with the details as it was an easy job requiring just a couple of new parts and the height adjust screw being shortened. I used brass for a bush and aluminium (type unknown) for the shaft as that's what I had in the junk box. The tilt adjust mechanism now feels rock solid and I have confidence it cannot easily fail.

20210127-200714
28/01/2021 00:50:50
Posted by Howard Lewis on 27/01/2021 11:45:09:

Possibly being pedantic, and sticking to prototype, what was the original thread? Possibly not Metric but Imperial or Unified? In which case it might be 5/16 rather than M8

If BSF or UNF would give a finer adjustment ( 22 or 24 tpi ) rather than 1.25 mm which is nearer 20 tpi.

Howard

5/16" was my original assumption and subsequently confirmed by measurement. I believe these Walker Turner bandsaws were made in the USA in the 1930s / 40s and that must have an influence on the threads we can expect to see.

Thanks for your contribution

26/01/2021 23:32:01
Posted by AJAX on 26/01/2021 22:43:18:
I've had a few more thoughts about a possible solution. If re-tapping / threading the hole is a problem then I could take an entirely different approach and turn a plug that fits in the centre hole (see photo below) and cross-drill and thread that plug. It's not quite as simple as it sounds, as the centre hole is used for the height adjustment, but that shouldn't be too difficult to modify either.
h3

I will probably be back...

As promised, I'm now back after having another look at the tilt and height adjustment.

The easiest, cheapest and strongest solution will be as mentioned above. I will turn a cross-drilled and tapped shaft to fit in the centre hole. The tilt adjust screw can then go through the existing dodgy thread before passing through the newly tapped shaft.

The hole is bored to accommodate the height adjustment screw and a spring (adds tension to the bandsaw blade), but springs can be easily added to the rods either side and then all I need to add is a small bush. I tried a couple of valve springs from my junk box and it worked fine, but stiffer springs would probably be even better.

It's actually much easier than I had thought.

I'll try to get it done one evening later this week.

26/01/2021 22:43:18
Posted by Neil A on 26/01/2021 22:23:06:

To be honest the remaining wall thickness after using an M8 x1,25 helicoil tap looks as though it will be rather thin from your photo. From the helicoil information it should be a minimum of 3,5mm but may not be enough if your assessment of the metal is correct.

Is there any mileage in machining out the existing poor thread and fitting a headed steel bush which has a plain 8mm diameter section, that is Loctited into the hole, and an M8 x 1,25 threaded end for a nut and washer?

Perhaps you could just fit a through bolt and Loctite that in position, I don't know how much room you have.

There does not look to be much metal to play with, it might require a bit more thought.

I hope it works out.

Neil

Thanks, Neil.

I've had a few more thoughts about a possible solution. If re-tapping / threading the hole is a problem then I could take an entirely different approach and turn a plug that fits in the centre hole (see photo below) and cross-drill and thread that plug. It's not quite as simple as it sounds, as the centre hole is used for the height adjustment, but that shouldn't be too difficult to modify either.

h3

I will probably be back...

26/01/2021 22:14:57

Thanks for the helicoil recommendations. I've never used one before but I knew they exist.

Measuring the internal diameter of the threaded hole (the "minor diameter" indicates about 7.64 mm. There's probably less than 1.5mm material to one side. I'm assuming the original screw was 5/16 BSW.

I just watched a YouTube video to get an idea about how a helicoil could be used. He drilled and tapped the hole, then installed the helicoil. No shortage of taps here but I'm not keen on enlarging the hole.

Are helicoils suitable for a through-hole? The screw must pass through the threaded section.

Any suggestions?

26/01/2021 20:28:00

Something else I forgot to add:

Would filling the hole with JB weld, drilling and tapping be a viable solution? I'd much rather fill it with metal.

26/01/2021 20:25:45

I have an old Walker Turner bandsaw that I'm finally getting around to repairing. I have all the parts but there's one thing I would like to fix before reassembly. The top wheel has an adjuster for tracking and it appears that someone stripped the thread and/or used an M8 screw. I don't trust the thread enough and don't want it to give way during use. Failure might lead to the top wheel making sudden manoeuvres.

Here is a closeup of the tapped hole. As you can see, there's not a lot of material to work with. It is diecast something (pot metal?) that goes with the era. The rest of the machine is very solid cast iron.

h2 h1
I have been tempted to mill this part down and make a replacement "lug". However, there's really not a lot to screw this lug into. If I have to do more complex machining I'd be tempted to make a new assembly of my own design but I'd rather a small job didn't grow into a big one.
If you want to know what it could look like, here is an example (not my own)
http://www.vintagemachinery.org/photoindex/detail.aspx?id=5286
Thanks,
Brian

Thread: Can you ID this vintage lathe?
24/01/2021 12:07:25
Posted by Rob McSweeney on 24/01/2021 09:07:29:

Iooks like a 5" Drummond to me.

Plenty of info on www.lathes.co, plus a group on facebook and what used to be a yahoo group which has now migrated elsewhere.

Thanks

24/01/2021 12:04:38
Posted by Ady1 on 24/01/2021 00:46:20:

A curious machine, big, but not heavy at the headstock end, an unusual box bed design and a powered cross slide absolutely brimming with t-nut slots

I agree, the bed design is unusual and not like anything else I can find. The cross slide looks like a boring table.

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