Member postings for Andrew Johnston

To a first approximation average over an integral number of circles.

Regards,

Andrew

The manual I have doesn't state that there are left and right hand versions of the threading/tapping attachments. So, out of curiosity, I've taken the tailstock capstan tapping head apart:

I'm impressed, a really simple design that presumably works well and reliably. I have a supplementary question. If I made a couple of dogs, one for the fixed part and one for moving part, with the opposite taper to that in the picture then presumably the head would operate with left hand taps?

Regards,

Andrew

Edited By Andrew Johnston on 08/11/2012 15:34:07

Hi Dave,

Ah, now I understand the operation of the Coventry dieheads! Presumably the threading/tapping heads work in the same way. For right hand threads, run the Britan in reverse until the stop is reached and the dog clutch disengages, then put the lathe in forward and back out the die/tap? I'm pretty sure that the threading/tapping accessories I have are for right hand; seems logical as I guess that they are the most common. I appreciate that you tended not to use the tapping attachments, but what sort of taps might have been used; hand, spiral point, spiral flute?

Right, next question, if you don't mind! Here's what I assume are the backstop parts, for second operations:

I wondered what the two lower items were when I collected everything; presumably they're extra backstops, of different lengths? I think I understand the principle of the backstop, but I'm not sure how it is fitted. On the top shaft presumably the collar on the left screws onto the headstock spindle on the left hand end? At the moment there seems to be a plain collar at that end on the spindle, although it does have a couple of holes for a pin wrench.

I'm keeping an eye out for Britan tooling, although I think it's probably a forlorn hope, as what tooling is likely to be around will probably be associated with a lathe; or nobody will have clue what it is!

Regards,

Andrew

Dave: Doooh, why didn't I think of that; I've got loads of timber down the side of the house that'll do fine for raising the lathe.

I'm not sure I follow the instructions for the Coventry dieheads. Does the lathe run in reverse, or forward, when the thread is actually being cut?

At some point I'm going to have to get a grip and actually set up and make something on the lathe!

Regards,

Andrew

Edited By Andrew Johnston on 07/11/2012 12:12:42

Hi Dave,

Is the body for the split die holders the right most part, under the lower shaft and to the right of the three split die holders? One of the split die holders was screwed onto it, but I took it apart for the purposes of the picture.

Regards,

Andrew

Indeed I have seen it. Here's a picture of the long taper (about 11.5" long) on the connecting rod being machined:

The taper is being cut with the aid of a hydraulic copy unit. The sheet steel pattern and follower can be seen bottom right. It is essentially the same idea as mooted by Phil. A couple of caveats I'd add are: one that the hydraulic copy unit has variable stops, so the workpiece can be reduced in a series of steps, rather than one go. Second, as the copy unit is at an angle to the lathe axis it can follow the pattern at right angles to the lathe axis to clear the big end, even though the feed is still engaged. However, I see no reason why the method suggested by Phil will not work.

Here's a picture of the two finished connecting rods:

Regards,

Andrew

Edited By Andrew Johnston on 06/11/2012 22:11:22

Hi Dave,

Thanks for the information. In due course I'll have a play with the dog clutch, just to see that it works. I've just discovered the first boo-boo due to the position of the lathe. I can't get the second shaft out of the tailstock because it clashes with the flypress on the right. If I cant the lathe round further to clear it I won't be able to use the bar feeder. At the moment my preferred option is to put the lathe on some standoffs, to raise it an inch or so. But I'll think about it before going to the trouble of making some. I'm not married, so I only have to worry about me going A over T over the bar feeder support; if I was married I doubt I'd be buying and playing with repetition lathes.

Right, now onto threading, here's a picture of all the threading equipment I got with the lathe:

Starting at the top are 1/2" and 8mm Coventry dieheads. I'm familiar with Coventry dieheads, and use them with the capstan unit on my conventional lathe. Presumably on the Britan these use the second shaft on the tailstock and utilise a stop, as shown on the lower shaft, to prevent rotation. My main question is about feeds, presumably the dieheads are used at low spindle speed and fed by hand until the dies bite. After that I assume that stops are set to allow the diehead to pull off and release the dies as normal?

The lower shaft I assume is also used in the second slot on the tailstock? At the moment it is set up with a self releasing holder for taps. Most of the small 'collets' below the shaft appear to be home made and are presumably for holding different sized taps? Again, I assume that the feed is by hand, until the unit reaches a stop and releases the tap. Next to the collets is what I take to be an adaptor for holding split circular dies. Does this screw onto the adaptor above in place of the tap holder?

At the bottom of the picture is what I assume is a self releasing tap holder for use in the tailstock tool turret? The tap in the holder is held in a split brass collet. I don't have any others of these in the bits and pieces, so presumably it is just a case of making one's own to suit as required?

Regards,

Andrew

If Terry is correct, and the shafts are EN8, then that is most likely your problem. I've found that EN8 in particular needs to be run faster than other steels to get a good finish with insert carbide tooling. Fast means the swarf coming off dull red, ie, hot! See this link for some detailed numbers on turning EN8:

**LINK**

Regards,

Andrew

Alternatively you can calculate the required starting diameter, so that the risk of 'doubling' is greatly reduced. The knurled pattern is effectively a very fine gear. Therefore, to fit the 'teeth' neatly around the circumference of the work the circumference needs to be an integral multiple of the tooth pitch on the knurl.

As an example, I've just knurled the caps for some oilers on the connecting rods for my traction engines. The nominal OD of the cap was 11/16", ie, 0.6875". The knurl wheel I used was 1mm pitch. I reduced the starting OD to 0.677", which gives a circumference of 54.02mm. The knurled pattern appeared with no 'doubling' or other problems.

There is plenty of information on the calculations for form knurling in Machinery's Handbook.

Regards,

Andrew

Looks really neat to me and a nice finish on the parts, well done.

Regards,

Andrew

Sam: I'm glad you've found the thread entertaining, although I wouldn't claim any of the glory. I'm just the novice here. I have wondered if the forum might find this thread a bit esoteric, although it's fascinating and very informative for me.

The compressor is definitely working on my lathe, as I can feel gentle 'puffs' coming out of the hole for the bar feeder air supply. In due course I intend to try out the bar feeder. The manual talks about using end plates and cotton thread for set up. Presumably this is just a couple of round plates with central holes that are used to stretch the thread through the bar feeder. The thread can then be ''eyed up' where it exits the bar feeder and enters the headstock, to see that it is central. Even I wouldn't contemplate permanently fitting the bar feeder outer support in my hall. Doooh, it's that H&S again, I don't really want to go A over T tripping over the bar feeder support! Instead I plan to fit it just inside the hall door, where it will be in the corner near the hinges, and therefore not in the way. I'll probably need a temporary outer support in the hall, or have to add a bit of weight to the bar feeder near the headstock. I see that Dave says that you can use the bar feeder with the spindle running. I hadn't thought of that, but it makes sense for saving time in production. I guess it could get exciting feeding a 1-1/4" bar on a reasonable speed range. I guess that's why the manual strongly recommends you have a blanking stop in the tailstock slots if they're not being used for tooling.

The coolant spray bar on my lathe can be adjusted for length, but the minimum is about 2", so I take Dave's point about using tape to block it off where required. I've got plenty of experience of spreading coolant around the workshop with my CNC mill; I don't really want to build on that experience. Talking of the dog clutch on the coolant pump, how do you move it? I checked the clutch to see if it was engaged when I was getting the coolant going. It was engaged, but it didn't seem all that easy to move, and I didn't manage it. Is there a detent or similar that needs to be operated before the sleeve can move?

It sounds like the speed change is a bit of a rigmarole. However, I will give it a go in due course, as it will be interesting to try the lathe across it's speed range. I have a set of spare belts, although whether they are a matched set is another matter. A couple of the belts have treasury tags with part numbers that agree with the Britan manual, but one of the B numbers doesn't agree. The manual says B30, the belt says B31. However, the belts on the lathe look fine, and I suspect that with the use I'll be giving them they'll last for ever.

I agree entirely with Dave on H&S. My comments were a gentle ribbing at those on another thread, where the OP had asked for a few ideas outside of model engineering, who jumped in warning of H&S Armageddon. While my workshop and machines do not meet modern H&S standards in terms of electrical cutouts and guarding, I do take H&S seriously. I have a fire extinguisher, first aid kit and eye wash in the workshop, and I always wear goggles when machining. As Dave says, it's all down to common sense and personal responsibility.

Regards,

Andrew

Edited By Andrew Johnston on 05/11/2012 11:24:08

Hi Dave,

It is possible to open the drop down cover sufficiently to see what is going on. If I ever needed to remove the auxilliary motor pack I'd have to move the lathe; but I'll worry about that if it ever happens. A minor reason for have the lathe at an angle is so that I can remove the coolant tank. Speaking of which, I've now got the coolant running. it took quite a while for the coolant to appear at the nozzle. The previous owner muttered about priming the coolant flow if the lathe hadn't been used for a while, but I'm afraid the technique went in one ear and out the other.

While fiddling with the coolant it occurred to me that the lathe would cause some of the H&S worriers on this forum to have a wobbly. When the coolant wasn't running I opened the drop down cover to see if the pump was running, or if the dog clutch was disengaged. No protection, with the system running there is the belt drive all ready to trap fingers! In the same way, the headstock can be opened while running, exposing the final belt drive.

I'd like to try the lathe on all the speed ranges available by moving the belt that drives the headstock. The only adjustment that I can seen is a screw/spring arrangement that attaches to the motor tray. Is this what I use to move the belt from one headstock pulley set to the next? The manual doesn't seem to mention changing speeds, just how to change the belt when it needs replacing.

Regards,

Andrew

Edit: That's the other thing I was going to say but forgot; the coolant flow seems quite 'weedy'. All the nozzles seem to be open, but the flow is a gentle stream. I was expecting rather a blast of coolant?

Edited By Andrew Johnston on 03/11/2012 12:07:01

No, but personally I don't worry about it. Whatever you do there's always someone who is better, faster, more skilled or whatever; that's life.

Regards,

Andrew

Hi Dave,

Once again thanks for the excellent information. I've now double checked the three phase wiring and moved the Britan off the rollers and into what I hope is its final position:

It is at a rather jaunty angle so that the tool capstan lever clears the bench, bottom right, albeit with a bit chiselled out of the bench leg. I can also still fully open the entrance door, always a plus, and the bar feeder is still able to extend through the door into the hall. At the moment the Clarkson T&C grinder is in the way, but it is only temporarily sat where it is. Once I've moved it, time will tell if the Britan is in the correct place. If it needs straightening up I'll have to make a new lever with a bend in it to keep it clear of the bench. In the bottom right of the drip tray is a small red plastic tea strainer. The previous owner was at pains to explain that this was to catch small parts as they were parted off!

The coolant tank is now in place, so when I get the chance I'll fill it with suds and check that the coolant system works.

I've been playing with the cross slide autolock. If I understand this correctly it is activated for parallel, or taper, turning where the tool doesn't move radially. If the set screw extends within the limits given in the manual the autolock will hold the tool firmly against the tool rest. For facing and parting presumably it is disabled as the tool is selected?

My next question is on profile turning. This is described by one sentence in the manual, which says use a profile plate in place of the standard tool rest. I have a hydraulic copy unit on my normal lathe, so I'm familiar with the basics of copy turning, but inevitably there are specifics that escape me. Does the profile plate replace the standard tool rest? If so, presumably it still needs to support the tool as well as having the correct profile. Can I assume that the profile is produced by having the cross slide in manual mode, held by hand against the profile plate, while feeding along with the hydraulic feed? On my hydraulic copy unit it states that the follower should have the same profile as the tool to ensure a faithful copy. How does this work if the set screw is used as the follower?

Regards,

Andrew

Edited By Andrew Johnston on 02/11/2012 10:39:01

I won't ask, I'll just say Bridgeport.

Andrew

Dave: One thing I forgot to ask in my previous post; would you use coolant when machining brass on the Britan, or run it dry as is the convention on manual lathes?

Regards,

Andrew

Dave: I'm not sure I have the theory yet, let alone the art! It'll be interesting to see how the coolant gets spread around. My lathe came with a small casting, with a clear window, that clips over the spray tube. As far as I can tell it's an original Britan part. The hydraulic feeds are definitely better, but still a little jerky at very slow feedrates, say 1/2 a turn from closed on the adjuster, so I guess I haven't quite got all the air out yet. I haven't looked the bar feeder yet. Due to the lathe location I can't permanently install the bar feeder, as it will have to stick through the door and into the hall. I'll have a play with it once I've got the lathe finally positioned, so I can operate all the controls, and still open the door from the hall.

Adrian: Thanks for checking the oil specifications. I'm mighty relieved that the ISO32 oil is ok, otherwise I've got 20 litres that's no use to me. As for the manual oiling points I've got loads of ISO68 hydraulic oil, so may be I should use that rather than the slideway oil. I'd certainly be interested in any advice, hints or reminiscences you have.

Clearly for turning parallel along the lathe axis the diameter is controlled by having the set screw on the tool capstan hard up against the tool rest. However, for operations like facing or parting off what role does the relevant set screw play? Is it just a limit to stop the tool going beyond the centre point? I assume that the feedrate, and hence surface finish, for facing is controlled purely by how fast the operator moves the handle?

I'm hoping to have a bit more of a play with Britan later this week. I've been tied up in the workshop for the last couple of days machining an experimental jig for a company that always leaves things until the last minute, and then asks me to work through the weekend.

Regards,

Andrew

Edited By Andrew Johnston on 29/10/2012 23:09:45

Hi Dave,

Thanks for the very useful hints 'n' tips. Clearly the accuracy of the tool centre height setting depends upon the skill of the tool setter! It's also great to have some numbers to aim for on length and diameter tolerances. I'm a great believer in numbers, they're a key part of engineering.

I assume by suds you mean soluble oil? That what the people I bought the lathe from used. The only Britan I have seen running (some years ago) was using neat cutting oil. I'd prefer to use soluble oil, as I that is what I use on my other machines, and it would be good to stick to one type.

Now onto hydraulic oils; the manual specifies Shell Tellus 27 or equivalent. This doesn't seem to be available now; it's either ISO22 or ISO32. I've bought some ISO32 hydraulic oil, as some companies list this as an equivalent to ISO27. I hope it will be ok, or I've got a lot of redundant hydraulic oil!

For lubrication I imagine it will be no problem to find the lithium grease specified. For other oiling points the manual says straight mineral oil. For general slideway oiling I use an ISO68 oil formulated for slideways; any reason why this shouldn't be fine?

Regards,

Andrew

Richard: Clarkson Dedlock holders seem to be cheap and in abundance on Ebay at the moment. I bought an INT40 version for £10. It means cutting an internal thread in the end of the arbor, but they may give a more positive drive than a Morse taper. I'm guessing your gears are around 4DP?

Regards,

Andrew

I bought a 1-1/4" arbor for my horizontal mill from Home & Workshop Machinery, but I assume you've tried them?

Two ideas spring to mind:

1) Machine an extension piece to fit the existing arbor, or make your own arbor.

2) Go the whole hog and use the undercutting method, although it would be a lot of work to make the accessories needed! Like this:

Regards,

Andrew