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Member postings for Scrim

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

Thread: Best Steel Type for a Toolpost
24/08/2011 12:08:00
I have a choice of:
 
EN1A Mild Steel, or D2 Tool Steel (annealed)
 
to make a set of lathe toolposts.
 
Would hardened tool steel give a noticeably sturdier support?

I get the impression EN1A is softer than the average bit of mild steel you find lying around. Would EN1A be tough enough to prevent threads stripping when tool clamping bolts are over tightened (M6, 15mm deep threaded hole)?
 
Thanks
 
Thread: Old Oxygen Bottles Use
23/08/2011 15:14:47
Thanks for the advice folks.
 
Adams Gas looks like my best bet.
Albee only seem to do Argon:
 
Cheers,
 
Alan
 
 
 
23/08/2011 10:43:40
If I buy an old oxygen bottle, will I be able to get it tested and refilled? If so, where could I take it and what sort of price would it cost?
 
Also, what sort of valves would I need to add to it? I'm hoping to put together a small oxy-propane brazing set that doesn't cost a fortune to buy or run.
Thread: Precision Tailstock Alignment
27/04/2011 02:56:48
Thanks again.
Currently my lathe is sitting on a flimsy desk using the basic rubber feet it was supplied with! It's better than a hammock, but not much! I'll be moving to its final location in a month or two where I'll really concentrate on fully setting it up.
 
To answer an earlier question, my Super C3 headstock axis of rotation is located 90.45mm above the flat areas of the bed when measured just in front of the supplied 3-jaw chuck. I measured it by facing a short bar in the chuck and lightly scribing three fine lines across its face with a height gauge, turning the chuck 1/3 turn between scribes. By trial and error, cleaning off the last lines with fine abrasive, I got all three lines to cross at one point as viewed through a 10x loupe, and then recorded the height gauge reading. As a rough indication of accuracy, a second measurement a few days later when I mistakenly thought I'd lost the first one came out just 0.01mm lower.
26/04/2011 00:55:19
OK, I really do need to check the headstock fitting and everything else, but I've come to this problem being happy with the way the lathe cuts in general and just wanting to make the tailstock usable for now rather than take on sorting the whole lathe alignment out at the moment, but I do understand the points made about this.
After further thought this is what I intend to do for now, until I get around to the full fix. I'll finish the job I started, fitting the lower part of the tailstock to the bed. Then I'll find what shims are required between lower and upper tailstock and epoxy these in place such that the tailstock is at least a lot better than currently. Right now I need the tailstock to do some work. When time permits I do the full check of my lathe alignment, identify what need to be done and then consider how to do it in the light of all the great help offered here.
Thanks again. I hope the discussion has been as useful to others as to myself.
Regards,
Scrim
23/04/2011 15:42:27
Thanks again for all the help. I feel confident I have all the issues in mind now and one way or another I'll get the problem solved.
 
The hand grinding technique I have in mind is described somewhere on the web for fitting a saddle to bed by using double sided taped strips of abrasive paper on the bed ways. Done carefully it can produce a very good fit, but it's a very manually intensive.
 
I mentioned the caliper just to illustrate that some parts of the lathe are accurate to 0.01mm whilst other parts can be out by 0.5mm.
 


23/04/2011 09:27:19
On second thoughts, my bed fitting technique is only for taking off small amounts of metal so I wouldn't want to try lowering the headstock myself. Instead I think I'll end up doing a good job raising the tailstock with shims.
22/04/2011 16:24:07
I think the theory that my tailstock got swapped with someone elses, somehow slipped through the system seems most likely. I very much appreciate offers of help (I live quite near Alexandra Palace in north-east London) but I'm fairly confident that my bed fitting technique is good.
21/04/2011 23:26:52
Ah! Normal posting has resumed!
 
 
Thread: Problem posting reply in this forum
21/04/2011 17:32:48
I can't post a reply to or look at the second page of this thread:
 
http://www.model-engineer.co.uk/forums/postings.asp?th=50541
Thread: Precision Tailstock Alignment
21/04/2011 17:11:18
I'm having trouble posting here for some reason. I'll try again:
 
Hi, Sorry for the delay in getting back. I agree that the error in my tailstock is excessive and I should have thought about asking for a replacement but at the time of purchase of this, my first lathe, I was a bit overwhelmed with all the other issues. Also, my experience of the number and extent of problems with my Super C3 left me expecting very little. To give an example, my first experience of improving part of my lathe was to work on the dovetail and gib in the vertical slide accessory I'd also bought at ARC Eurotrade. There was a big problem with the set screws that position the gib as their threaded holes were drilled too high so that the gib sat not flat against the opposing dovetail surface, but tilted at an angle. The result was that the gib made only a line contact with the dovetail face instead of pressing on it with its whole surface. I questioned the boss, Ketan, at ARC Eurotrade about this. He passed on his top mechanical chaps opinion that it wasn't worth trying to fix this problem on the vertical slide. I ignored this and redrilled/tapped three new holes and then a few spent days with silicon carbide grits lapping the dovetail/gib surfaces together and it now has a truly superb action.

After that experience I could easily understand why ARC's preparation service for my Super C3 included redrilling/tapping the set screws for my cross slide gib - it clearly had the exact same problem! I also noted the same saddle gib screw fix on the Super C3 shown on 'The Society of Model and Experimental Engineers' (SMEE) stand at the Alexandria Palace Model Engineering show earlier this year, so sadly it seems they mass produce them with this fault as standard! Ketan says it's a long hard slog getting them over in China to improve anything. The guess is that the jig they use to drill the set screw holes is out by millimetres due to extreme wear. Operating a wobbling drill press sitting with it on bare unsurfaced ground is a potential cause! I should point out that some parts are made exactly accurate as as far as my new Mitutoyo caliper can tell, so the range of machining quality very variable.

Returning to the tailstock: I decided to practice my intended technique for hand grinding the saddle to fit the bed by grinding the lower section of my tailstock to fit the bed first. As supplied it only made contact at one point on each of its three contact faces so there was plenty of room for improvement. Having already begun this regrinding I don't feel in a good position to ask for it to be replaced and anyway, I'd just have to repeat the very laborious bed fitting again (you do it with cut strips of silicon carbide sandpaper...).

OK, so this situation is a joke, but on the other hand I got a compact lathe with the new quite sophisticated high torque at low revs speed controlled motor for a small fraction of the cost of something like a Myford, which would be too big for me anyway. The best way to get the Chinese to get their act together is for some other up and coming county to outclass them at a competitive price. Meanwhile people will grin and bear it as alternatives are limited when so too is cash.

Thanks for all the input. I’ve had a suggestion that after checking everything else I might lower the headstock instead of raising the tailstock and this would certainly result in a much tidier solution that I’d foreseen, so I may follow that course.
17/04/2011 00:50:51
Thanks for all the replies. I should first correct an error in my original post - it should read: "The next step would be to somehow fix the

TAILstock in this position relative to its base."

I should really leave the precise setting of my tailstock until the bed and headstock are checked, but for now I definitely need to do some work on the tailstock as it's about 0.5mm low, which strains small drills and with larger drills results in over sized holes and the drill only cutting on one of its edges.
 
I'm aware of the usual methods of aligning the tailstock, but thought my approach might have advantages. I've realised though that it won't account for any error in the direction the tailstock moves when you turn its handle
 
Turcite sounds interesting. Where could I get it?
 

 
16/04/2011 01:54:20
I’d like my SC3 tailstock to be really accurately aligned to the headstock but there are four degrees of freedom to deal with: Vertical/Horizontal displacements and Vertical/Horizontal angular errors (technically called Yaw and Pitch I think).
It looks hard to adjust all four, but I have an idea to deal with the lot in one go.
Turn an MT2 taper (to match my tailstock) on a mild steel bar held at the headstock by any rigid means. The taper will be exactly concentric with the headstock axis of rotation so when the tailstock is fitted on it, it will also be precisely positioned on the headstock axis of rotation, as required.
The next step would be to somehow fix the headstock in this position relative to its base. It’s tempting to just fill all the gaps with shim and epoxy it solid, but it would be better if the tailstock could still be offset but easily returned to be exactly on axis at any time.
Has anyone seen an approach like this? I’m looking for ideas for this last step of the process.
Thread: Improvements to the Mini-Lathe Half Nut Mechanism?
26/02/2011 19:50:36
Thanks folks. For now I've made do with the following which has improved things a lot:
I fitted a large diameter thin spring washer between the apron and the 'cam' type disk that's rotated by the engaging handle.
I cleaned up the face of the handle which bears on the apron by facing in the lathe (with no apron you have to hold the saddle against a bed stop and use the top slide to feed the tool to the left).
I replaced the two soft washers which hold the gib in place with two strong steel 'washers'. I used the ends of the two feeler gauge strips that already had holes bored in them so all I had to do was cut off with a Dremel and clean the edges up.
 
With adjustment of the gib it now has a smooth and precise feeling action.
It doesn't appear that using a single half nut detracts from the mechanisms function, so I won't worry about that as I like having the guard to keep swarf off the lead screw. ARC actually offered to send me the upper half nut when I bought the Super C3, but I decided not to take them up on it for some reason.
 
Scrim
21/02/2011 17:25:20
Fear not - if I come up with anything I'll pass it on one way or another!
 
Scrim
21/02/2011 14:53:07
Thanks John,
 
It's a good point about the half nut mechanism being well down the to do list! I wouldn't have bothered looking at it if I hadn't already been working on the apron. Also, it does seem my mechanism is a little crankier than some as a friend says they don't get the sticking problem I experienced.
I'm tempted to just try to get it working as before (not necessarily a trivial exercise!) and get back to the both more important and more easily fixed issues for now.
 
Scrim
20/02/2011 22:20:41
Looks like I might be on my own with this one then!
 
Scrim
19/02/2011 17:42:45
Whilst adding a plastic chip guard behind my SC3 mini lathe apron I decided to strip and improve the half nut mechanism. In the case my 'Super C3' (SC3) it's more a case of a 'half of a nut' mechanism in fact as only the lower half of the usual pair of half-nuts is present because the new leadscrew guard doesn't leave any room for the upper one. It still seems to engage and drive the saddle ok, but I found the engaging lever would often stick so I wanted to improve it.
 
I also noted the usual mini-lathe problem with the dovetails and gibs making poor contact so I expected to make some marked improvements by lapping them to a better fit.
 
However, the more I study the mechanism the more I think the manufacturers need to redesign it from scratch. It's quite a surprise it works at all as far as I can tell. Virtually all the dovetail in contact with the half nut is missing on one side where a circular recess has been cut for the cam type (?) mechanism that the handle turns, and on the other side the gib is held in place by two screws+washers. It looks like a total bodge and I suspect any minor attempts to improve it may stop it working by what ever mysterious means it currently functions. Are there any articles out there about this issue and ways to resolve it, because I can't find anything beyond a mention that the mechanism includes a gib?
 
Scrim
 
 


Thread: Which slideway oil is best?
19/02/2011 01:10:00
I looked into slideway oils myself recently as I just bought my first lathe (Super C3). First I bought some Vactra No.2 but was surprised by the very strong sulphurous smell when I sniffed the can. As I have my lathe indoors I didn't want it stinking the house out. I've since discovered that the smell only seems to accumulate significantly in a sealed can as I left a dish of it out for a few days and I couldn't smell it at all after the first day. Still, I was concerned it might result in a subtle unpleasant smell only visitors would notice, so I decided this was another beginners expense I'd have to take on the nose and tried the next suitable oil I came across called Slideway 68 from Chronos. It's very innofensive smell wise. To me it smells and looks very much like modern car engine oil, but it seems to work so I've stuck with it. Talking of sticking, that's what slideway oils are supposed to avoid. If you notice a 'stick and slip' effect when moving slideways, perhaps you should try one of the recommended oils. If engine oil doesn't 'stick and slip' then I'd guess it's probably as good as the specialist stuff. Any ideas on what to do with a litre of smelly Vactra No.2?
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