A couple of lathe questions

[njl]

Hi everyone,

I'm very new to machining and joined the forum the other day. I have subsequently added a few pictures of my machines to my welcome post if anyone who asked for pictures wants to see them, they are there now.

My lathe is a Colchester student 1800. It is an imperial machine. When I bought the machine it didn't come with a manual but I subsequently found one on ebay. It seems to fit pretty well with my machine and shows two thread indicators an imperial one and a metric one. My machine is fitted with the following indicator which the manual shows as a metric type.

Inside it has a range of gear wheels available for different threads. It turns OK when the lead screw turns so the teeth mesh OK with the imperial lead screw but is it correct to have a metric indicator on an imperial machine? Currently I'm doing all my threading keeping the half nuts engaged and reversing the tool after each pass. I sort of assumed an imperial machine would have an imperial indicator and a metric machine a metric indicator or does this type of indicator do for both imperial and metric threads?

This brings me on to my second question. The second photo shows the brake peddle on the machine.

When I press on this peddle the power is cut off to the motor and a rubber brake block is pressed up against the head stock pulley. The lathe takes a few revolutions to stop. Therefore I always need to withdraw the tool from the job or the tool will hit the head of the bolt I am making or I need to make very long waisted part to the bolts. As a second test of the brake, if I drill a hole in a piece of stock held in the chuck and then tap it by hand, when pressing on the brake peddle the chuck can revolve when the tap starts cutting hard. Is this correct or is the brake knackered. I'm thinking it should be more effective than this but I appreciate there is going to be a fair bit of momentum when the chuck is revolving so I wouldn't expect it to stop instantly.

Thanks for your help,
Nick

 

[njl]

Here a couple of extra views of the thread indicator

The plate on the side

The different gears

 

[Kermit]

The lathes at work(the small ones) which have that type of brake, stop within 1 revolution of the chuck. At least that what it appears like to my eye. I would guess your brake is not gripping the shaft like it should. And it might take longer to stop, if the piece in the chuck is of substanstial mass.

As for the indicator, I'm not sure about that.

Kermit

 

[ksouers]

Hi njl,
Welcome to HMEM.

My first production job was using a Clausing-Colchester lathe identical to yours, though a bit larger. On that machine the motor ran all the time and used a clutch to drive the chuck. The clutch was operated by a red-handled lever on the carriage apron. This was connected through linkages to the brake peddle. Stepping on the peddle would disengage the clutch and apply the brake. And, yes, it took several revolutions to stop. This clutch lever was pulled up for normal rotation of the chuck, and pushed all the way down for reverse rotation.

Tapping was done at slow rotation. When the tap reached bottom the clutch lever was pushed all the way down to instantly reverse the chuck and back out the tap.

Also on the apron is a lever to operate the carriage feed. This lever is engaged and disengaged while the chuck is turning. On the left side of the apron was a button of sorts that would disengage the carriage feed when it hit a stop. Very handy when you wanted to make repeated cuts to the same length or threading to a shoulder.

If I understand correctly from your description it sounds like you are engaging the carriage feed and attempting to stop the carriage feed by stopping the chuck. It's not necessary to stop the work from spinning to disengage the feed. Just release the feed lever then back up the carriage, set your next cut and engage the feed again.

I'm not familiar with the metric thread dials, so I'll leave that to one of our metric gurus.

So, recommendations: Check to see if you have the quick-reversing clutch system. Also, see if you have the carriage feed disengage button on the apron. If so, I highly recommend making up an adjustable stop you can clamp on the bed ways. It will make life oh so much easier. Get used to using the carriage feed lever to start and stop the carriage moving.

Hopefully I've been of some help to you.

 

[steamer]

One assumes you have a "D" or "A" spindle mount.........?

I trust the chuck is not mounted on a central thread?.....that could get ugly with a fast stop......with the chuck unwinding itself from the spindle.

Dave

 

[ksouers]

Dave,
Good point!
Looking at the wide-angle shot in his "Welcome" thread it looks like a D-series mount, so no problems there.
It's been some 30 odd years since I last ran the Clausing-Colchester I couldn't recall the chuck mount.

 

[Tin Falcon]

http://www.metalworking.com/tutorials/army-tc-9-524/ch7.pdf
This should help a bit good info on lathe operation and a decent section on threading. And a nutshell guide attacked.
I think . some can correct me here but the gear that is an even multiple of your lead screw pitch may work.
at the very least you can cut srcews that are an even multiple of your leaad screw without an thread dial. ie a 8 pitch lead screw will cut 8,16,24,32,40, ...tpi
Tin


View attachment thread dial guide.pdf

 

[njl]

Thanks for the input guys and the pointer to the Army manual.

Yes the lathe has a D1 type cam lock so the chuck can't unscrew.

The reason I was wanting to stop the lathe between threading passes was so that I can keep the tnuts closed throughout the operation as I'm unsure what the thread indicator is telling me.

The lead screw has a 4 tpi pitch.

When I was taking about the brake not holding with taping operations I meant that I was manually turning the tapping tool into a center drilled hole and the brake would not hold the chuck still.

On my lathe the motor doesn't run all the time; when you operate the red lever, down is forward, middle is stop and up is backwards. When you press the brake the lever is not affected but the motor contactor drops out and the lathe wont go again until you move the red level to the middle position and then reselect the direction.

I have once moved the lever from forwards to reverse and the lathe stopped instantly and then went backwards. I'm not sure if that is a legit operation I was in a panic at the time working a piece very close to the chuck!

In the manual I got from ebay it also talks about bed stops. Here are a few shots of the saddle. I can't see any buttons for a stop to press unless the top lefthand corner is something. It is a square bar part covered by a screw.

The lhs side of the saddle

a close up of the top left corner- maybe the stop presses on this. I did try running the lathe with feed and pushing on this with a screwdriver but it didn't stop the feed. I don't feel happy to try and stop the carrage by letting it run into something fixed!

This is the front of the saddle, the two black levers control the feed, the button selects feed to the cross slide or main carrage.

This is the right side of the saddle and shows the red lever for direction control.


Thanks again for your help.
Nick

 

[Jasonb]

Depending what pitch thread you are cutting you need to have the correct cog on the indicator and then only use the drop in numbers for that thread.

eg if cutting a 5.5mm pitch thread you need to use the 22T cog and can drop in on either position 1 or 3 so don't need to keep the nut engaged.

Does sound like the brake needs some adjustment if you can turn the machine over with a tap wrench while the brake is applied.

Jason

 

[Tin Falcon]

The lead screw has a 4 tpi pitch.

fantastic so you can do many common thread pitches without even needing a thread dial as long as the thread pitch is evenly divisble by 4.
Tin

 

[ksouers]

Nick,
Ok, I understand what you were trying to do now. Sorry for the misunderstanding.

That screw is for adjusting the front gib. There should be another on the back side. The square bar is the gib itself. It doesn't look like you have the tripper for the carriage feed. That's a shame, it's such a handy thing to have. Still, making a stop and/or indicator holder is a good idea.

That threaded hole in the carriage is curious. Is it mentioned in the manual? The 30 year old memories are fuzzy, but I don't think the trip was that high on the saddle.

Yes, sounds like the brake might need some adjustment, though it's purpose is not to hold the chuck still but simply slow the chuck down quickly.

 

[joeby]

The Clausing lathes I have seen/ worked with didn't have a trip for the feed, just a simple turret stop. The threaded hole mentioned would most likely have had a threaded post screwed into it for the stop to bear against. You would normally disengage the feed a short distance before the stop and hand feed to the stop. The screw you mention is indeed the gib screw.

As far as the spindle brake goes, I remember setting up the brake on a 15" Clausing lathe that specified a complete stop in 3 seconds or less from 1500 RPM, I believe that was with the 3 jaw and no workpiece.

As a little reminder, DO NOT start a lathe with an empty chuck unless the jaws are tightened against one another, at high speeds a fast start can cause the chuck to rotate while the scroll remains stationary and the jaws will open. I have seen the jaws thrown out of a chuck this way, believe it or not.

Kevin

 

[ksouers]

Nick,
After a bit of reading that jogged my memory I believe the trip was an internal detection, i.e. the carriage encountered resistance that tripped the feed. Nothing external that tripped it.

You can find more information about the Colchester line here:
http://www.lathes.co.uk/colchester/ though I'm sure you've already visited it.

Kevin,
The lathe I worked with was actually a Colchester but with a Clausing badge on it.

 

[njl]

Thanks again for all the help guys, I've learnt a lot from all the little gems you have given me over the last couple of days.

joeby - I had no idea about the danger of running an open chuck either!

So in summary, I need to fix/adjust the brake. I don't need to use a thread indicator to do common imperial threads but just need to use it for the metric threads. I need to pluck up the courage to try out a bed stop - I'll experiment and hand crank the machine into a stop and check it works OK that way.

Ksouers - the manual does show the threaded holes on each end of the saddle but there is no mention as to what they are there for. It is not as detailed a publication as I would have liked, better than nothing but it leaves a lot of things undocumented. I used the www.lathes.co.uk site to research the lathe before I bought it so I didn't look a complete plonker when I went to do the pre-delivery acceptance inspection.

Nick

 

[Tin Falcon]

IIRC when I worked at the air base we had a modern style south bend that had similar holes in the saddle for stop blocks there were large safety stop switches that would prevent accidental over travel of the saddle in auto feed mode. kind of like limit switches on a CNC.
The 16 t gear should work fine for imperial threading. My sb has an 8 pitch screw and 32 teeth on the dial so the ratio is right. then use the chart I gave you.I learned when in doubt always engage on the #1
Tin