What have I done wrong?

[Peter G. ShawParticipant @peterg-shaw75338]

[Peter G. ShawParticipant @peterg-shaw75338]

I ahve a Warco Minimill which I bought some years ago. At that time I was a complete ignoramus about milling machines, ie I could recognise one but that was about all. So, this was then in the nature of an education for me.

Unfortunately, as I found out too late, this machine has proved to be a mess, eg the slides where visible were nicely done, but when I dismantled them, I found that the non-visible parts had been partially formed with an angle grinder. This, I feel is tantamount to fraud by the manufacturer but other than informing Roger Warren, who to his credit did say that they had stopped selling this machine due to all the problems they were getting, there is not a lot I can do.

Anyway, I am now slowly attempting rectify matters.

Todays problem concerns the fine feed for the vertical slide. This is a worm engaging with a wormwheel which in turn engages with the coarse feed by means of a multi-tooth dog clutch. (I think that is the right term.) The worm and wormwheel run in a support block which is rather crude so I am attempting to make a replacement.

The worm is at the end of a rod which about 55mm from the end has a flange formed on it. This flange sits in a recess in the block and in turn is held in place by a keep plate. Thus the worm is more or less located in a set position. The worm od is slightly less than 12mm, the shaft is also slightly less than 12mm, but slightly larger than the worm, whilst the flange is 15mm dia and 3mm thick.

To create the hole in the new block, I drilled a 7/16 in blind hole appropriately deep – I do not have any metric drills above 10mm. I then reamed it 12mm and followed up with a 12mm silver steel D bit. This was because I discovered on a practice aluminium block that the reamer is tapered. On the aluminium practice block, I got the worm and shaft to reasonably easily fit. On the steel block, it will not. The recess is 15.1mm diameter so there should be sufficient clearance there. The depth is more than adequate. I push a 12mm dia aluminium rod into the hole and it does not go full depth without jamming. In addition, there is evidence using this bar, of air lock which suggests that the hole diameter is very, very close indeed to 12mm.

Any ideas about what to do next? And what I may have done wrong?

At the moment I am thinking about drilling right through, reaming from the other end, then soft-soldering a plug into the end.

I should also point out the new steel block was BMS and being a bit wary of warping due to making unequal holes in it, I have attempted to normalize it by heating it to a high temperature and holding it there for an hour – it is 25mm thick.

Also, all the work on the hole, drilling, reaming, D bit has been done with the block mounted in the 4-jaw independant chuck. It has not been removed, indeed it is still there as I write. Furthermore, inserting the worm shaft as far as possible and switching the lathe on shows the shaft, all 160mm of it, to be running quite true so all the indications are that all the work is in fact concentric.

Regards,

Peter G. Shaw

[Keith LongParticipant @keithlong89920]

Peter

If I've interpreted your message right it sounds as though you've got to the stage of having a slightly tapered hole in the block. To relieve the air locking phenomena you could try drilling a very small hole though the bottom of the block as an air releif passage, although once you get the fit on the worm shaft right you won't need it.

How close a fit do you REALLY need on the worm shaft. A thou or so clearance won't really upset the meshing of the worm and wheel and will just marginally increase the backlash, which you will have anyway as the worm and wheel will have to have clearance to be able to turn freeely.

As the job is still set up in the lathe can you perhaps ease the fit on the hole by polishing with some fine emery paper on a suitable support, or if the fit on the "open" end of the hole is ok perhaps take a very fine cut with a boring bar at the blind end of the hole, possibly deliberately forming a small indercut to ensure that you're not getting hung up with a small radius at the bottom of the hole and sqaure end to the shaft.

As an aside, I've only tried using a D bit once and got a tapered hole then – I need more practice!

Good luck.

Keith

[LambtonParticipant @lambton]

Peter,

If you have try using a new I'm end mill as a reamer or a good quality new 12mm drill may help.

I appreciate you may not wish to purchase any new items but I have built up a useful range of drills and milling cutters over the years by purchasing single items as I needed them. I fell you frustration at not having the correct bit of kit and consequently improvising with less than satisfactory results.

Eric

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Peter ,

Reamers mostly have a relatively long lead in taper . The only common exception is the machine reamer which has a very short lead in taper – often just a little chamfer .

Your D bit will have lost its edge almost immediately it touched the work and got progressively worse as you continued into the bore . Silver steel D bits will only work properly on steels at very low cutting speeds – otherwise cutting edge gets hot and loses all hardness .

Try again with a D bit . Newly sharpened and tempered to straw it should work if you keep down to very low speeds – and we might be talking about 50 rpm max or even turning chuck by hand .

Plenty of cutting oil ( or any oil ) .

Otherwise do as suggested and ream right through or bore out .

Regards ,

MikeW

[Michael GilliganParticipant @michaelgilligan61133]

Peter,

If the design permits … I would definitely take the hole right through.

Perfect solution is then to use a "between centres" boring bar, with the job mounted on the cross slide / boring table.

MichaelG.

[Peter G. ShawParticipant @peterg-shaw75338]

Keith,

I had wondered about using fine emery, or even wet n' dry, or even lapping powders especially as I have some left over from David White's suggestions in MEW150.

I would have tried a boring tool ecept for the inconvenient fact of not having a suitable one readily to hand. Interestingly, I have been looking at some Soba boring tools as advertised by Chronos which come in various sizes from 3/16 inch upwards. I certainly think the smallest could be useful.

Eric,

I have already tried a new 12mm endmill. I am also considering buying a set of metric drills to cover 10.5 to 13mm rising by 0.5mm, the reason being that I only have imperial above 10mm.

Michael Williams,

I discovered about the taper when I made the practice aluminium block which is why I created the D bit.

Despite the fact that I then mucked up the D bit either by overheating, or by dropping it when fully hard and thus causing it to crack, it does, rather surprisingly, still work and cuts on the end – as it should, or so I believe. Speedwise, I used the lathe at 125rpm – its minimum speed, and yes it did get warm, but not hot. Even so it still cuts. And yes, I did use loads of cutting oil.

In respect of overheating, I discovered that the shank of the D bit was oversize by up to 0.05mm although the actual cutting tip was correct at 12.00mm. I have checked what is left of the original silver steel bar and that is dead to size so it looks as if during heating it has swelled somewhat. I have read about this somewhere, Tubal Cain I think.

Both Michaels,

I think I will drill & ream right through. I think this will be easiest in the long run.

To everyone.

Thanks for confirming what I suspected, ie that something has gone taper.

So, back to the lathe & get it opened up whilst everything is still lined up.

For what it is worth, my ultimate intention is to run the works in grease eventually so I will have to keep gaps to a mimimum.

Regards,

Peter G. Shaw

[Ian S CParticipant @iansc]

A small boring bar would be the way to go, but if you deside to ream right through, you could fit the plug with loctite retainer rather than trying to solder it, even thread loc would do for that job. It is a bit of a bother when you'v got to build your own machine, but at least you'll know it well. Ian S C

[Sub MandrelParticipant @submandrel]

Hi Peter,

If it is the same basic mechansim as on my (rather better finished by the sound of it) X2 this 'fine feed' mechanism is the weakest part of the design. The backlash in the worm and wheel wil remain very large, whatever you do, because of the fit of the gears. I minimised (reduced would be a better word) backlash by squeezing up all the sections of the universal joints in a vice, this removed about a quarter of a turn of backlash!

Good luck

Neil

[Peter G. ShawParticipant @peterg-shaw75338]

Ian SC,

I originally thought about loctite, or even my favourite, Araldite. But then I thought that perhaps soft solder might be better. Still time to rethink though. Thanks.

Neil,

Yes it is similar – except that there is no universal joint. If there had been, that would have eliminated one of the problems which is that due to the slope of the side of the headstock casing, the spindle, when located within the support block at the front is under some bending moment thus causing a tightening and difficulty in operating. As a temporary measure, I inserted a shim between the rear block and the headstock and this helped. I am now trying to improve on that. There is a thread about this showing what I did elsewhere on this site – look for a thread on Disassembling of MiniMill… started by MarcuSweden and on the third page are some photos from me showing what I did.

I do indeed doubt that I will ever get rid of the backlash, but I would like to be able easily operate the fine feed.

Regards,

Peter G. Shaw

[Peter G. ShawParticipant @peterg-shaw75338]

Wey-Hey, I have done it!!!

I have an old length of HSS, so old that I do not know how old it is. And I am even guessing that it is HSS. You see, it came with my first lathe about 20 years ago. Anyway, at some time in the past it had been roughly ground to be a small diameter, about 4 to5mm, and about 45mm long tiny boring tool with a moderately large portion for clamping. So what I did was to grind some more off to lengthen narrow bit, apply to the hole, out came a tiny amount of swarf, and in popped the shaft to full depth. Problem solved.

But then another silly problem developed. The flange, according to my Starrett 0.01mm precision dial caliper, and my Rolson 0.01mm precision digital caliper is about 2.95mm thick. The recess it sits in, is 2.94mm deep according to the Starrett or 3.00mm deep according to the Rolson. Looking at it in situ with the aid of as much magnification as I can muster, and the recess is definitely deeper then the flange so the Starrett would appear to be wrong.

Both calipers were zeroed before measuring by closing the cleaned jaws then twisting the dial/pressing the zero button to measure the flange, or to measure the depth by extending the bar and then using the flat lathe bed pressing the body down until both sides of the end of the body were in contact with the lathe bed. Then the dial was rotated or the zero button pressed as appropriate.

Measuring with the jaws a piece of scrap steel, and both calipers show the same which seems to suggest that for some reason the Starrett is under-reading on depth measurements. Most odd.

Any ideas?

Regards,

Peter G. Shaw

[Sub MandrelParticipant @submandrel]

If the inside of the flange is slightly angled and they have different sized probes, this could cause the difference.

Neil

[SpringbokParticipant @springbok]

Me I would scrap it sell it on fleabay (that is what that site is for) and purchase a decent little mill.

Bob

[Peter G. ShawParticipant @peterg-shaw75338]

Neil,

I have had a good look and cannot see anything. That does not mean that there is not anything' just that it is not visible.

Bob,

You are probably correct – except that in its present state it is more use to me as an educational aid than it is to anyone foolish enough to buy it.

Interestingly, because it is somewhat dismantled, I am having to use the vertical slide on the lathe for milling – which is one of the reasons I bought the machine in the first place, ie to avoid having to use the lathe.

Still, it is all good fun.

Regards and thanks,

Peter G. Shaw

[Author]

Posts