Aug 19 2010

The new milling machine

One of my brain-relaxing passtimes is to randomly browse ebay for interesting machines, broken items for spares/repair and so on. Like Thomas Edison said; “To invent, you need a good imagination and a pile of junk.”
Of course Edison didn’t have access to ebay or Google Image Search, so while I have a nice pile of junk, I can add a whole lot of extra random inspiration to it by just browsing images of junk.

One of my searches is usually for mill or lathe parts, to see if there’s any out there I could put to good use. I’ve been hoarding parts with the hope of building a mill or better milling accessory for my Conquest Lathe. Even a second-hand tiny mill will still run to well over £200, so my best chances of getting something within my tiny budget are:

  1. Find a machine so broken it’s cheap, but damaged in such a way I alone can fix it at very little cost.
  2. Find parts of other machines that I can assemble into a working milling machine.
  3. Find a machine strange enough that few other people will bid on it.

Last week, Option 3 occurred on one of my browsing sessions. And I won it.

Small Homebuilt Milling Machine In need of attention to bring it up to a good standard the drive pulleys do not match exactly , although 2 or 3 speeds are available

there is play in the rise and fall of the headstock and a clearance problem with raising the head fully , maybe a bit of re-design needed!

the table has been fitted with a thrust Bearing and 1 end modified to accept a power feed unit but was never fitted

the table and / or the headstock needs a bit of shimming to get true machining

heavy fabricated steel construction with 370 Watt 1/2 Horse Power Single Phase 230 Volt Motor with Full Overload Protection and remote Stop/Start Pushbuttons

A good quality Cast Table , Size 475 x 154mm (Table cost was £100 ) 1/2″ MT2 Chuck with M10 Thread Drawbar Tilting Headsock ( left / right )

Adjustable Taper Bearing Headstock overall height of machine is 960mm depth is 600mm table to chuck height Max. 250mm Weight aprx 120 Kilos

Some light water marks to table due to garage roof leaking but not serious

please ask any questions i can e-mail more photos if required

£50 delivery on a pallet OR collection from Braughing , near Ware , Hertfordshire OR arrange your own collection

Mainland UK delivery only NOT to the Highlands or certain places in Wales,please ask

Payment by Paypal Only within 3 days of auction end

Happy Bidding!

A home made machine! Perfect!
Collection verses a £50 shipping fee would further lower competition, and it was just 30 miles north of me. And while I don’t want to offend the builder of it, the punctuation in the description probably doesn’t inspire the confidence for others to give that extra bid.

All in all, a prime listing for getting a bargain. And at £155 for 13,700cm3 of machining capacity, that’s a bargain in my books.

Now while I’m going to have to discuss the machines faults, I again don’t mean to offend the builder of it. It’s in my estimation the same sort of machine I’d have built in 18 months or so, with a few hundred quid in parts and the same development feel (initial planning, careful use, leading into jury-rigging just to get it finally working). So this machine has saved me a year and a half and a hundred quid or so. So I can skip straight into taking this messy but functional machine and refining it.

Collection

My mother kindly gave me a lift up last Saturday (Aug 14th) in her van to make the collection of the machine. We got there fine and got it loaded with the help of a forklift. Loading it on a pallet didn’t work, as it was too wide for the wheel-wells, so it was unscrewed from it and loaded bare.

One of the mounting brackets snapped off at that point. Some rather weak welds, looking rather “last-minute-thought” held a piece of drilled angle iron to the main frame of it. But not a problem. I have a couple of welders afterall.

Installation

120Kg is not something I can lift by myself, and even if I had a forklift of my own, I’d have to drive it through some barriers, bushes and a very tall fence to use it in getting the machine in one piece to the workshop doors.

I got out the spanners and unbolted the machine into three large chunks. Not something easy to do on a commercially available machine of the same capacity.

From the strain in my shoulders, I should probably have gone for four pieces! But this made it manageable to load onto a sack-barrow and move through the house into the workshop where I could bolt it back together and dream of a long hot soak in a bath.

Investigation

The machine’s still new to me, so after putting it back together to make sure it survived the journey (and welding the mount back on) the next thing I did was take it apart again.

For ease, I’ll divide the investigation up into the Base & Vertical, the X-Y Table, and the Headstock & Motor.

Base & Vertical

The base is made of some very well welded bits of structural steel channel, joined to form an L-shape. The mounts are tacked on each side near the back, and two strips have been machined flat where the table is to rest.

Those flats were my first note to correct. While they fit the sides of the X-Y table, the weld seam at the front where there’s an overhanding extension to the base is still proud enough to foul the bottom the table. So a couple of delicate swipes with the angle-grinder helped get the table seated better. It still needs more grinding, but it’s a lot better than it was. I’m wondering if this is why the table apparently needs shimming, according to the auction?

The vertical slide is bolted to a 90-degree mount that is in turn bolted to the upright U-channel that has a plate welded to the end.

The four outer bolts seem original to the slide, but I’m not so sure about the middle two. Also the bracket has “ningr” welded into the surface. The only word I can find that that’s a part of is “uningratiating”, which just makes it plain cryptic. I don’t yet know if the mount is part of the machine the slide came from too, or if it’s an original construction.

The slide is mounted very high. Maybe the previous owner was using a very large milling vice? The chuck can reach the table surface, but only at the point where it’s falling off the slide.

In some post-sale email with the seller, the vertical slide apparently came from a “multi-head tenon machine”, which would explain it’s single-ended design and bolt-on nature. I’m imagining a number of such slides all being configured and being used at once on a large parallel bar system.

The slide itself doesn’t seem to have it’s original leadscrew. It’s centred on the slide bed, but not the saddle. In fact the saddle isn’t centred either. The saddles cross-slide mounting groove has also been crudely ground off on the lower end, apparently to make room for the rotary mount.

In fact, if you notice from the pictures, there’s an extra hole on the right-hand side, but the lock is protruding from the left. And there’s two more holes on the left side too. The saddle is also offset to the right, and the leadscrew is to the left of that hole in the middle that looks like it should have the leadnut attached at.

I’m pretty sure that this slide is intended to have two gibs, one on each side. That would account for the extra holes, the off-centre positioning and the extra hole on the right which is supposed to have the lock installed in.

It goes without saying then that the leadnut at least isn’t in it’s original position. And seeing as there’s nowhere else it’d fit with the ~5mm offset, it must be another modification.

With the large countersunk (on both sides) hole in the middle, I suspect it might have used a nut with a wedge backlash adjustment. I’ve read that this is a rare sort, so combined with the double-gibs, this is an odd bit of a machine.

The only bit upsetting this theory is that the 4 apparent bolt holes are recessed on the back side of the saddle, not the front. That would suggest the hole is the mount and adjustment for the cross-slide. But it’s not centred on the vertical. Maybe the holes have been partly drilled out? Or maybe the original nut had some locating nubs? Likewise, maybe only the center hole is original and the rest are drilled around it? Something seems to have been bolted over it from the front though.

Some of the holes on the front of the saddle seem precisely positioned and original. It makes me wonder if cross-slide wasn’t passive. Knocked into place and secured, while the depth adjustment was done by leadscrew. It would explain the shallow depth of the guides on the front.

The leadscrew in use also doesn’t seem likely to be original. I thought a 2mm pitch was odd, until I noticed it had a V-profile. The leadscrew is a standard M16 thread. Not something used on large machines.

There’s also a bit of a knock in the thread near the bottom.

The slide has a couple of tapped holes at the top end, so mounting something easier to use than the current handle should be possible.

So the slide needs:

  • A stop
  • 2 new gibs
  • A new leadscrew & nut
  • Front face machining smooth
  • Brake moving
  • 90-degree gearing for easier height adjustment

The rotary mount doesn’t have a lot to say about it by comparison. It’s made of aluminium, is secured in place by three bolts and is apparently there mostly to increase the mills throat depth. Which is understandable with all that table travel.

It’s pretty sturdy, but has some gouges in the inner track from where bolts have been driven through to mount it to the slide. I forgot to check, but suspect it’s designed to bolt-on from the rear.

Two slide bolts and one regular hold the millhead-plate on. Again forgot to check, but I think the originals are imperial bolts while the new one is metric.

Having this option seems useful, but on machines that can rotate the head it usually means the millhead has it’s own height adjustment so it can plunge at that angle. The head on this machine is fixed, so if it can be lowered enough to find the workpiece, all this can do is cut bevels really.

Headstock & Motor

The headstock is rather long. It’s a very solid piece of steel box-section with welded end-plates. Those end-plates have the bearing mounts allen-bolted to them. On top is the pully with three steps.

Off to the left the end-plate is wider at the top so a side-arm can be bolted on. The side arm goes around the side of the vertical slide where the motor mount slides onto the arm. It’s held in place by some more bolts, but can be slid up and down the arm to adjust belt tension. There is a middle pully on a swing-arm mounted on the arm which takes the belt feed around the side.

When the vertical slide is wound up, the adjustment handle fouls the motor pully, limiting the range of the vertical motion. Some of the mounts on the motor-slide are also rather suspect looking,  and heading into the “just to get it working” area mentioned.

The pulleys are also mis-matched and poorly aligned as a result. The auction wasn’t wrong when it’s “2 or 3” speeds. How much do you feel like wearing out that drive belt?

The motor is 370Watt or 0.5HP if you prefer, so it has a decent bit of grunt. If I can get the gearing sorted, it should help a lot.

  • Motor and drive belts need repositioning
  • Ideally want fine depth control at the headstock
  • Graduated and controlled rotation of the head assembly

X-Y Table

The X-Y table there were mistakes about in the listing. On the plus-side, the travel of the table was under-reported. I recorded it at Y-axis having 194mm of travel, X-axis 353mm. And the X would have gone a bit more if the handles were a fraction narrower.

The bad mistake is that the table isn’t metric, it’s imperial and graduated into 10ths & 100ths of an inch (this was stated in a direct reply from the seller that wasn’t reposted on the auction). The Y-axis leadnut is also very worn, to the point that there’s about 2/10ths of an inch of slack when you turn the handle, and the leadscrew turns eccentrically. But I can wear this mistake. It can be converted to metric and the nut changed at the same time.

The paint on the base is actually my biggest worry at the moment. It flakes off in sharp chunks all over the place. I’ve also noticed one of the gib-adjustment bolts has been sawn off. There should be enough to grab ahold of to get it out though.

It also takes huge 1-inch T-nuts.

But it’s a very sturdy base to work from. The X-axis nut is cast in place, but I’m confident I can work out a way of removing it and replacing it with a metric nut. The Y is just bolted-in.

  • Needs stripping down and repainting
  • Burrs and chips to the casting should be filed away to prevent point-stresses
  • Drill and tap rear mounts on Y-axis for future CNC use and better screw mounting
  • Convert to metric
  • Try and gain 16mm on Y-axis for “A4 paper size” machining capacity (even if this will mean bolting a larger table to the main table)
  • Re-tap current holes to convert all fixings to metric?

Priorities

The X-Y table needs to come first really. The head may be visually nasty, but having a well configured X-Y table will make making replacement parts for it a lot easier. It’s also the least involved part to do. The head needs a comprehensive re-design.

For the head, I’d like to get my hands on a broken pillar drill. From that I can re-use the drive quill and its splined shaft with pulleys. I can mount the motor upside-down and reverse it’s direction and mount it over the top of the rotating mount. I’ll have to make the throat deeper for that too.

The splined shaft will mean I can make a depth-adjustable head for it.

If I use a nice stiff axle for it all to rotate on with some decent bearings, I think I might be able to get away with gutting a cheap 100mm rotary table (~£50 on ebay) to manage the controlled rotation. Will mean making sure it’s all well balanced though so it’s only moving the mass, not the weight once it’s off-centre.

The intial priority though is knocking together some vice-clamps out of angle-iron and getting the table calibrated well enough to handle making the new bits for the X-Y table conversion.

Will have to hunt down some lumps of steel to work from, I only really have bars and box-section.

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