Member postings for David Oyns

Hi All

Thanks very much indeed for your very prompt and very sound advice. I shall try the suggestions and see what happens. The housing in question, Chipmaster part 1473 (cover), has a ridiculously thin bolting face at one point (1/8" but this is above the oil level when the machine is at rest.

Wishing you all a happy, successful and virus-free New Year.

PS: I did wish to send a pic but when clicking on the picture icon to the left of the camera some crazy text in Latin comes up. Being an uneducated ex-North Yorkshireman (the border was moved making me a 'Clevelander'!) I was unable to decipher the text. Anyone have the same issue? Shades of Non illigitimum desperandum carborundum!

David

Good morning.

I have a Colchester Chipmaster lathe which has a feed gearbox. It has been plagued with oil leaks despite frequent changes of '0' rings and gaskets. Some months ago I replaced both and placed a sheet of 'tell tale' paper towel under the housing. Occasional checking showed no loss whatever. The lathe had not been used for a while then yesterday I noticed oil seeping under the machine and opening the rear cover I found the towel saturated. The tooth belt spindle was dry - clearly the 0 ring was fine - but the mating joint with the main gearbox was clearly wet. All the allen screw were tight - in fact quite difficult to undo.

On removing the cover and examining the paper gasket it was much discoloured and appears to have been acting as a wick, drawing oil through. The gasket had received a smear of Hylomar on both sides. Thinking this was inferior paper gasket material I removed it to find on the other side the trade name 'Flexoid', the oil resistant gasket material.

I have ordered Flexoid sheets in various thicknesses. Is there anyone out there who has had and overcome this problem? Should I use a thicker gauge? should I fit the gasket dry or is there a better sealant than Hylomar? My next step will be to check for distortion of the housing but I think this very unlikely - the gasket was of uniform thickness. The oil is the recommended ISO 68 hydraulic oil. Any ideas?

Hi

Just a note to say that, having followed the advice above, the carriage does now stop when striking the bed-stop, so very many thanks for the advice given.

I was unable to make the adjustments with the apron on the lathe - too limited access - but removing the apron (and feed bar/leadscrew) is so quick that it's not worth the fight. I found the adjustment screws very tight and had to be super-careful when holding the pinion with a large screwdriver to oppose the torque of the allen key. I did note the original positions as advised (depth of the adjustment screws in the shaft) using a vernier and put the readings in a safe place.

The adjustment made was a quarter turn in each case. The release was slightly more firm than I would have liked but perfectly workable. I may make a further adjustment, perhaps an eighth of a turn if I have the apron off again.

One word of caution - when replacing the apron the first time I tightened the screws, then found that the wheel was jammed - the pinion had not meshed with the rack. Luckily no damage to rack or pinion. I'm now very careful to check engagement before screws are tightened., moving the carriage to ensure free movement.

Thank you, DC31K. Super advice which has done the trick.

David

Dear DC31k

I am very appreciative of your considered reply and advice which I shall follow.

The carriage with feed engaged does push the bed stop along the bed. I have given it a fairly firm tighten but possibly not 'a good yank'. Could you please convert that spec into a torque setting? (chuckle!)

One tiny mod I've done is to remove the welch plug which prevents access to the interlock bar by drilling, tapping, then pulling out with a bolt. This done, the plug has a small allen screw fitted which can be removed and a 'puller' bolt employed when the interlock bar needs to be removed again - as I've done several times while trying to fix this issue.

Great tip to measure the position of the screws. This is something I would, of course, have realised...….. AFTER adjustment! You may well have saved me a great deal of time and frustration by mentioning this.

I wonder if you are right by mentioning the bed stop tightness - perhaps I'm being too timid. When the machine was in service in my school workshop the kids didn't seem to have a problem!

Why do I have the machine and several from the school workshop here at home? - because an idiot HM decided that such facilities were 'not really the image the school wishes to promote'. No wonder so many these days do not know which end of a screwdriver to use! The machines should be back at school motivating the students who loved making things and appreciated the skills they learned. End of soapbox!

Well, I'll close and follow up your advice. Many Thanks for responding, so good of you.

Kind regards, keep safe.

David

Dear Fellow Engineers

I am aware of a post on this subject in January 2020. I have a Colchester Chipmaster lathe on which the carriage assembly fails to disengage at a bed stop when auto-feeding. I have tightened the stop moderately but never allowed significant pressure to build up - too many posts in various manuals of sheared gears or racks.

I have changed the apron assembly, tried two different latch castings and associated gears, etc,. checked that the 'knock-off pin' (Part 1905) is free, lubricated all moving parts, checked the movement of the bar (see next paragraph re hole spacing) with which the latch engages, checked each moving part for free movement and each gear mesh for correct play.

The apron casting has the serial number G 2011. It originally had the bar (for latch engagement) fitted solid to the casting, lacking the springing with parts including 1949,1850. I then discovered that the bar on this apron had a hole pitch of 1 1/8" rather than the 1 1/4" which appears standard. Furthermore the holes in the apron casting were simply countersunk unlike the 1 1/4" version which are counterbored to accept part 1850 - shoulder bush.

I modified the G 2011 casting with counterbores and opened the original screw clearance hole to accept the shoulder bush. The pitch was machined dead size and the bar moves without binding against the spring.

I've now run out of ideas - can anyone advise? I appreciate that there is the need to allow pressure on auto-feed when taking heavy cuts; the issue is just how much pressure should be allowed to build up when a bed stop is placed in position - and how would it be checked or regulated.

Thanks in advance - and if you respond to this during this current lock-down do, please, keep safe.

David