Preparing to buy a Colchester 2500?
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It is essential to bear in mind when you look at your potential purchase that it will most likely need some work to become reliable and accurate. Consider at all times that if it is missing bits or showing excessive wear, whatever you need to buy is either unobtainable or only available at eye watering prices.
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It needs to be understood that the chance of finding a perfect one is near to zero since all these machines will be used & some will be a lot more used than others. They were designed to remove cubic metres of material in a 24-hour working day, so wear is inevitable on a well-used machine. Bearing that in mind, buying a lathe can be a journey which you can enjoy if knowledge and planning has prepared your choice.
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Tools you will need:
Micrometres and/or a digital Vernier calliper
A dental mirror & a pencil torch-as an alternative a bore scope is the ultimate tool.
A long, large wooden or plastic handled screwdriver
What to look out for-firstly let’s look at the potential deal breakers or good points to use as leverage when bargaining.
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1. Bed Wear
Wind the saddle from headstock to tailstock feeling for tightness towards the tailstock compared to near the headstock. Check whether the gib adjusters (fig) are loose, tight, or no longer have any adjustment. Measure the bed thickness at the headstock, midway and at the tailstock (Fig) and compare the results.
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2. Main Drive Bearings
When the main drive bearings deteriorate a heavy rumble can be heard when the main motor is running without the main spindle rotating. Not too expensive and reasonably simple to replace.
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3. Lay Shaft Bearings
When one or more of the layshaft bearings are worn the noise will vary depending on the chosen gear.
Not too expensive but requires substantial effort to strip down. (Our manual can help you do that!)
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*Note*
Carefully placing a long rod or a large, long wooden, or hard plastic which is more comfortable, handled screwdriver against the bearing caps and your ear with the chuck rotating under power will help identify failed bearings.
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*Note*
It is advisable to remove the chuck to lessen the potential to injure yourself.
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4. Spindle bearings
Spindle vibration, squealing or excessive heat from the headstock when the main spindle is rotated under power is almost certainly an indication of spindle bearing failure. The spindle is carried by a pair of Gamet extremely high precision roller bearings & are the principal source of the lathe’s rotational accuracy.
The main spindle does not contain seals, prevention of debris ingress is achieved by using a nose cover with a V shaped internal space featuring a drain at its base. The bearings are very expensive but reasonably easy to replace. (Our manual will help you do that!)
Assuming that you haven’t walked away at this point then it’s essential to consider the following.
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5. Cleanliness & Corrosion
Some of my other documents mention the “bad jet wash”. Colchester lathes have many oilways to enable the distribution of lubrication which unfortunately also permits water and suds (water soluble cutting oil) to enter places that they should not go to.
Remember that oil is lighter than water which means water ingress will pool at the lowest points. Water and ferrous metal are bad partners so if you suspect a jet wash or suds contamination then be prepared to find rusting parts under the multitude of sheet metal covers & also in the apron. It’s location in the workshop can also have an effect, especially if located near to a south or west facing window, because the machine can warm and cool.
This can lead to condensation in the headstock, so if you can remove the top cover to peek then do so because it will prevent any surprises later. If you remove the sheet metal covers, expect every nook & cranny to be crammed with swarf, tightly packed in & probably congealed into lumps like the coconut in a bounty bar, held together with solidified cutting oil. Swarf can cause excessive wear because it tends to congregate behind the carriage, under the saddle at the back of the apron.
Ensure that the small sheet metal half nut cover is in place because that will prevent some swarf ingress. Expect the swarf contamination to cause excessive wear to the rack & to the rack pinion so be certain to look out for it with the dental mirror or borescope.
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6. Wear to moving parts.
The feed shaft wears more towards the headstock end than the tailstock end does. You can measure the diameter at each end & at several points along its length with a 0-1” micrometre. That isn’t a big deal because it is a 3/4” diameter ground steel bar and something that you can make when you get the lathe home and installed. It is a simple matter of turning the ends & cutting a long keyway with a milling machine.
The feed shaft slides through a precision bore in the pinion shaft at the rear of the apron which has an internal key to engage in the aforementioned keyway. The pinion shaft bore wears & the key has been known to be completely worn away. That pinion is available, but the cost is likely to be several hundred pounds at least.
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The pinion that engages the rack to traverse the saddle wears. The rack teeth fill up with swarf so check it carefully. The pinion is available but again it will cost you several hundred pounds to buy it. (It is possible to remake/repair that part with commercially available components.)
Cross-slide feed screw wear. Check it for tightness at the extreme ends of its travel because the thread wears in the middle over the most used portion. Again, a new screw is available at a cost of several hundred pounds. There is a backlash adjuster incorporated into the cross-slide feed nut, but it won’t compensate if the screw is excessively worn. There have been reports of users purchasing a length of acme threaded bar & grafting it onto the splined end of the cross-slide screw to replace the worn thread which can be considerably cheaper than purchasing a new complete screw.
Tailstock-barrel corrosion & scoring externally & internally on the morse taper together with a sloppy fit to the tailstock casting. New barrels occasionally appear on eBay etc. but be aware that a replacement barrel may not slide straight in. A little honing may then be required if changing barrels unless your tailstock bore is worn oversize… ouch!
As previously mentioned, the leadscrew half nuts fill up with swarf, especially if the small steel cover over it has been removed and not replaced. Check the leadscrew for visible excessive wear but since it is only used for screw cutting it should be OK.
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The control lever (forward/reverse) on the apron can feel extremely sloppy which can be due to wear in the square hole in the sleeve shaft, which slides along the square control rod, that it pivots on. However, it is more likely to be wear on the pins that the lever swivels on because they take quite a battering & can wear away to mere shadows of their former selves. It is possible to upgrade these pins by remaking them from 8mm silver steel. The pivot holes in the sleeve and the lever then need to be reamed out from 5/16” to 8mm. That will remove a lot of the sloppiness, restoring the machine to having a more positive feel of the controls.
The linkage through the bed to the clutch lever at the back of the headstock also gets very sloppy with use. All the pins are 5/16” diameter and they all wear, so it is a simple exercise to ream all the holes to 8mm and remake the pins from 8mm material. One 300mm length will suffice for the whole machine with some left over. It makes a huge difference.
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Is the machine fitted with a foot brake? If so, fixing a none working brake is relatively straightforward unless the brake has been removed completely.
If it doesn’t have a foot brake, then it should have an electromagnetic brake automatically operating each time the control lever is. Sometimes though the foot brakes have been removed from the machine because they have ceased to work. The way to tell if the machine has had that done is to check the row of switches along the front of the headstock. If there is a switch next to the coolant pump switch showing a brake symbol, then the machine came from the factory fitted with an electromagnetic brake. If there is a warning light instead of the switch, then the machine was originally fitted with a foot brake. On a machine fitted with an electromagnetic brake the chuck spindle should stop rotating almost instantly when returning the control lever to the centre position. If it does not, then the brake is either malfunctioning or the friction disc has been removed completely. We have a strip down of the brake by Alan Bryan on the site here (www.latheworkshop.co.uk\) on rebuilding the unit.
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Clutches-The machine should accelerate from a standstill to 2500rpm within a few seconds with a Chuck fitted according to the handbook. Likewise, when the control lever is moved from forward to reverse, pausing at the centre position, it should stop and accelerate to 2500 rpm in reverse within a few seconds too. If it doesn’t then it may just be an adjustment issue but if parts are needed such as clutch plates, then Matrix are available from a supplier advertising on the internet, but the cost is at least £1500 so be wary. Ortlinghaus clutch plates may still be available but it will be necessary to contact Ortlinghaus to ascertain that. Expect to pay a lot for new ones.
There is also a chap manufacturing them on eBay that may be worth a look.
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7. Health Checks
Check every speed in the headstock and listen carefully for odd noises which would indicate worn or missing gear teeth. Each speed should engage cleanly. If it doesn’t then it could be either worn selectors which can be remade or damaged gears which are probably due to someone changing gear with the machine running. New gears are available but again at a cost of several hundred pounds.
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Check the screw cutting/feed gearbox as for the headstock. The same issues can prevail, and the remedies are similar.
Electrics - The small enclosure for the switches mounted on the front of the headstock behind the screw-cutting speed chart fills with oil. It can also fill with water if a jet washer has been used. It may function ok but should be checked before putting the machine into use. Switch replacements are probably available if you care to hunt them down but expect to pay through the nose for old/new stock.
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The electrical enclosure at the rear of the headstock can also suffer from swarf & oil ingress. If the machine has been jet washed, then it may also have water in it. 400 volts & water are not good bedfellows so check carefully before proceeding.
Lubrication-The oil pump in the pedestal can be problematic for leaks and a worn and/or slack drive belt. Early machines had a jockey pulley tensioner for the belt, but later machines had no adjustment.
The headstock “dry sump” tank in the pedestal holds 11.4 litres (2.5 UK gallons) of oil. Budget to change that oil because it has probably been ignored. It is also possible to fit the machine with a replaceable cartridge filter which should be thought of as an essential conversion in my opinion.
(There may be a post on this)
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8. Oil leaks Generally
The apron gearbox leaks if the bottom gasket is shot. It can be remade from sheet gasket material as can the gasket on the feed gearbox or purchased from www.LatheWorkShop.co.uk. Leaking oil seals on the gearbox, headstock and apron are also available from www.LatheWorkShop.co.uk.
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9. Conclusion
This is not an exhaustive list but has hopefully given you food for thought. The difference when buying one of these machines when compared to the round head generation machines is that they are generally too new to find many that have been scrapped & broken for parts. That can leave you in the hands of the profiteering & unscrupulous who may have access to used or remade parts.
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