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12-20-2013, 04:15 PM #1
Colchester Chipmaster Thread Cutting HELP! LH 10TPI BSF on lathe without reverse
Hello, im jonpaul from County Durham, N.E UK. I have a small amount of experience with metalworking lathes, used to use a Barker. Recently bought an imperial chippy and ive messed around for a few days to farmiliarise myself with it. One project I recently just began was to start making faceplates for various woodworking lathes, mainly my own Harrison Jubilee which doesn't have a bowl turning faceplate. This plate is an internal left hand 1" 10TPI BSF thread. So ive made up my 60degree cutting tools from HSS and ive practised on some scrap bar beforehand. This practice brought forward a whole host of problems that have really knocked my confidence in any part of this thread cutting process. Before I began I figured I had it all worked out, until I began cutting and realised the following.
1) What I though I understood the TPI and gear charts just doesn't seem to figure out right as the actual thread being cut doesn't correspond at all to the chart. I had selected gear selector number 4 of 9, and the ABC selector gave me an option of either A or C as both on the chart produce a 10tpi, but in practice both cut a 9tpi, just short of 10tpi.
2) Also working out when to engage so that the cut drops in at the exact, precise point at each pass is proving problematic, despite understanding how the saddle is moved up and down the bed by using the thread dial. The problem to me seems to be that the chuck to me doesnt seem to be synced with the leadscrew? Im making this presumption upon limit knowledge by the way. The only thing I can think of resolving this is by setting up the whole machine ready to make a first pass and marking the chuck, leadscrew and saddle positionupon the bed and making references after each pass when setting up again? I know this will resolve my problems, but at the same time I know that this machine doesn't have to be used in this manual way, but working out the correct procedure of this process for this chipmaster is going over my head at present and im needing some help.
Also having to cut this left hand internal thread without this lathe having a reverse isn't the easiest of first projects, as firstly I have to cut from left to right and from within the workpiece, which you cant really see, or is indeed limited even if you leave a small gap between the piece and the chuck.
The way that I was having to cut this practice thread just didn't seem to work right at all.
I would benefit an awfull lot if to fully understand all the controls, the charts and the chippy way of cutting threads if you could help me out here. Their seems to be little on the net that explains and no tutorials on youtube. Ive read the manual which has left me with only a very basic knowledge, but not a great understanding of the controls and the process. The crazy thing is the manual explains the basic functions of the controls and then goes into crazy expert theory on multistart threads and some advice on gears etc for metric threads on an imperial machine?
I would be a very happy guy if I am not resorted to having to throw in the towel and shell out a small fortune on taps to do these weird and wonderfull threads just because I don't understand the tool already at my disposal that can invariably allow me to do the job.
Thanks very much and look forward to hearing from you sometime soon.. JonPaul
12-20-2013, 04:28 PM #2
I would suggest you start by sorting out why you are getting 9 tpi when you want 10 ,chances are that the gears on the end are not correct ,they may have been set up for cutting metric or some unusual thread,check in the manual what the gears on the end train should be.
Once you sort that ,using the thread dial indicator will work (it won't at the moment if the gears are set up for metric).
cutting a left hand internal is actually easier than right as you position the tool in the groove first and run out into fresh air ,which is aesier than trying to run into the groove .
Trying to tap the threads,even if you had a tap, would actually be more of a nightmare.
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12-20-2013, 05:00 PM #3
If what is supposed to be 10 tpi is turning out 9 tpi, check the end gearing behind the big swinging cover on the left end of the lathe. It sounds like you could have the gearing set for metric threading, as by incorrectly engaging the middle compound gear of the end gear train. You want the 33-tooth headstock output gear to engage the 55-tooth half of the idler gear and the 66-tooth gearbox input gear to engage the exact same 55-tooth half of the idler gear, not the 65-tooth gear that is attached to it. You may need to flip the 66-tooth gear. If you look at Page Title, and scroll down just past halfway on the page, you will see two arrangements of the idler 55/65 compound gear. You want the arrangement shown in the lower photograph. The upper photograph shows the arrangement for metric threading (which is actually only approximated metric threading).
On all lathes I've ever encountered, the threading dial stops if the carriage is being driven by the leadscrew, which is what happens as soon as you engage the half-nuts. In other words, the thread dial behavior you describe sounds normal.
Why no reverse? That's a pain, especially if you were trying to cut a metric thread, because you wouldn't want to disengage the half-nut.
12-20-2013, 05:27 PM #4
I will have another look at it Saturday. Its really disheartening when you seemingly know the thread cutting process, but trying to implement that through the machine and having other things completely throw you off completely. Then being left frustrated and confused. I will check the gears and see how its setup, maybe its setup for metric as you say. That can be the only real answer for why the charts aren't producing the threads that the machine shows it set to.
I think after working out how the gears are setup I will do some more practice threads. To workout how I eventualy got a 10tpi thread I had to mark the chuck at a point and I taped a ruler to the bed of the lathe, then when I counted 10 revolutions of the chuck as the leadscew had progressed the saddle 1" then I knew I had 10tpi.
I was having huge problems getting the cutting tip at the precise point at each pass without having any such markings upon the leadscrew, chuck and bed to re-align it all, as earlier I was having trouble understanding the thread dial indicator, but I think after this evenings research and videos ive viewed im of a better understanding. I was of the idea the dial stayed in contact with the leadscrew so you could see how far to rewind, but I was nt releasing the halfnut, I was simply reversing the machine with the leadscrew forward and reverse lever.
One thing that has come to light to me this evening for this constant miss aligning of each pass is that maybe the use of the clutch is allowing the chuck to become totally miss aligned and out of sync of the whole timing critical cutting process. As I have noticed that when stopping at each pas to then reverse the carriage back to begin again, the chuck will freewheel a little when slowing. Ive just learnt this eve that the Chipmaster has a brake that when slipping the clutch if you move the lever quickly further left it is supposed to stop the chuck dead?
Im sure I will get al this sometime very soon and look back on this as one of those confusing, stupid moments when something so simple, yet seemed so hard. But their is little on these Chipmasters online, few tutorials or videos. If any of you guys could knock one up it would be worth its weight in gold.
12-20-2013, 05:32 PM #5
The lathe motor only powers it forward (chuck anti clockwise). It either hasn't had this arrangement from day one or the whole reverse setup, including lever on the back of other Chipmasters isn't their at all. All I can do to reverse is by way of the leadscrew. The chuck I only have going in one direction. If it had a revesre this thread operation im so stumped with would be so much easier as its a thread straight through the internal piece and after each pass im guessing I can simply stop and reverse the whole process and it would then cut in both directions as I would have a bi-directional chuck. Which leads me to another question, if you throw a machine into reverse via the motor and the chuck goes clockwise, im gathering it to be common sense that the leadscrew also follows suit.
12-20-2013, 06:54 PM #6
You really need to sort out your lathe's electrical switch and get that motor turning backward if you are going to single point a left hand thread.
In the USA, I can buy a 1"-12 or 1"-8 UNS left hand tap for $39.10 (24 UK pounds). We don't have VAT either. Maybe you should ask Tracy Tools if they have your tap. Contact Us
12-20-2013, 10:17 PM #7
No, no, no, don't use the leadscrew reverse lever to go back to the beginning. When you flip that lever, you are momentarily disconnecting the gears inside the gearbox, and you lose the synchronization between the headstock spindle and leadscrew. On the other hand, you can start, stop, brake, and slip the spindle clutch all you want and the leadscrew will not go out of sync. Since you are cutting a 10-tpi thread on an Imperial machine, you can open the halfnut at the end of each pass and wind the carriage back manually. Just be sure to re-close the halfnut on any line on the threading dial.
12-21-2013, 01:36 AM #8
Oh that's great thanks.. I think I am getting to the bottom of the source of so much of Fridays confusion regarding my the non sync of the thread cutting practices I was carrying out.
Your right as ive checked this, when the clurch is slipped any further movement of the chuck slowing don't matter as it is still in sync with leadscrew. Its flipping the leadscrew from forward to reverse that's throwing it all out. Im sure Saturdays attempt at some practice threads will be far more succesfull.
Though I could still do with a little help with something of a brief of a couple of grey areas of the Chipmaster.
1) on the threading chart on the machine it is separated into two sides, the left being a feed rate in inches and the right side is actual TPI numbers for threading, their is also a section in a separate orange/red colour that shows some decimal numbers? What this for
2) Also on this threading chart on the left and right side charts their is a picture of some lever positions which I imagine are relative for setting to obtain the selections indicated below this. The left shows a lever pointing right at roughly 115degrees, on the right column shows two levers stacked ontop of one another, the top one being in a similar position to the first ive just explained, if not around 10 degrees shorter and this has another showing directly below it which shows to be what im guessing pointing upwards at around 75degrees, see the two yellow circled areas in the first picture here. I have not a clue as to which levers it is trying to explain? Can anyone tell me?
3) In my next example picture the lever in the orange circle which is stated as the Hi/Low speed selector would this primarily be set to slow for threading and high for facing tasks, drilling etc
4) The lever in the yellow circle is the Feed/Thread lever. I gather that this is pretty self explanatory and you thread when thread is selected and anything else that needs working on without the need for the powered leadscrew is to be done with a setting of Feed>
5) In the blue circle is the lower bar below the leadscrew, I gather this is what powers the saddle feed only? Either cross feeding or longitude feeding?
I have also noticed that the machine pictured, like mine doesn't seem to have a reverse lever behind the headstock? Would I be able to get away with adding a forward reverse selector switching unit to my electric motor? Do most electric motors allow you to power them this way and do they work in reverse from these switches that are pretty inexpensive on Ebay.
12-21-2013, 03:22 AM #9
[Quote. So ive made up my 60degree cutting tools from HSS and ive practised on some scrap bar beforehand[/quote]
Once you get the chippy's gear box sorted, don't forget that BSF is a 55 degree whitworth form thread!
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12-21-2013, 03:33 AM #10
The clutch slipping will not affect the positional relationship between spindle and tool but using the leadscrew reverse to reposition the tool does change this relationship.
Other than this, having a metric ratio in the pick off gears will ensure that the numbers on the thread dial are not useful.
Dunno about the chipmaster but the students and triumphs of the period had an electric motor reverse. Sounds like yours hasn't got this? and it may be something to do with the drive setup used on chipmasters.
If the motor is 3 phase it is readily reversed by reversing two of the phases.
12-21-2013, 04:11 AM #11
The entire saddle unit is identical to the Bantam's saddle... you are using the lever on the left of the saddle to engage the halfnut and not the lever in the bottom middle of the saddle?. I did that only once while not thinking and got some weird threading results.
12-21-2013, 05:24 AM #12
Are you sure you have the backgear engaged for screwcutting? This is required. I think you referred to it as hi /lo speed selector. The orange circle lever should be up to engage back gear.
12-21-2013, 07:45 AM #13
Are you sure it is a left hand thead? If the lathe spindle turns in the conventional anticlockwise direction when looking at the faceplate from the tailstock end of the lathe, the faceplate will almost certainly screw itself off the lathe spindle nose if the spindle nose and faceplate have LH threads unless there is some way to positively lock it onto the lathe spindle. This may happen either when you start the lathe or start to turn a workpiece, whereas a RH thread will tend to tighten the faceplate on the lathe spindle as you work.
Afterthought added later: Or is the faceplate for mounting on an extension of the headstock spindle on the outer end of the spindle for turning large diameter objects, in which case the LH thread is, of course, correct.
12-21-2013, 02:36 PM #14
If the lathe spindle turns in the conventional anticlockwise direction when looking at the faceplate from the tailstock end of the lathe, the faceplate will almost certainly screw itself off the lathe spindle nose if the spindle nose and faceplate have LH threads unless there is some way to positively lock it onto the lathe spindle.
I AM HAVING TO CUT A LH THREAD WITHOUT A REVERSE ON MY LATHE, WHICH MEANS I HAVE BEEN HAVING TO MAKE MY CUTS IN A BACKWARDS MANOR. ie FROM LEFT TO RIGHT, (IN OTHER WORDS IM HAVING TO START MY CUTS WITH THE CUTTING TIP SET DEEP INSIDE THE WORKPIECE AND ITS ACTUALY CUTTING LEFT TO RIGHT, MOVING FROM INSIDE THE CHUCK, THROUGH THE WORKPIECE AND OUT OF THE FRONT OF THE PIECE. THATS WHAT BEEN MAKING IT DIFFICULT! LUCKILY ITS A THREAD THROUGH THE COMPLETE 2" PIECE OF STEEL SO I DONT HAVE TO WORRY TOO MUCH ABOUT WHERE IM STARTING MY CUTS FROM, SO LONG AS ITS PAST THE PIECE IM FINE, WHICH I CAN SEE AS IM SPACING THE WORKPIECE A FEW MM AWAY FROM THE CHUCK FACE SO I CAN SEE THROUGH THIS GAP WHEN THE CUTTING TIP IS THROUGH AND I CAN STOP IT AND MAKE READY MY NEXT PASS.
I THINK MY CHUCK HAS SOMETHING CALLED A CAMLOCK DESIGN, KNOW LITTLE ABOUT THIS IF IM HONEST, NEVER YET REMOVED IT TO TAKE A LOOK, NOT HAD THIS LATHE 2WEEKS. LOOKING AT THE CHUCK IT HAS A LARGE 1.5" SLEEVE ON THE SPINDLE THAT THIS CHUCK IS CONNECTED TO AND THIS SLEEVE HAS I THINK 4 LARGE SQUARE BOLTS THAT ARE REMOVED WITH THE SAME TOOL YOU TIGHTEN YOUR CHUCK, THIS IS WHAT LOCKS THE CHUCK TO THE SPINDLE. I DONT THINK IT SCREWS ON IN THE WAY YOU DESCRIBED, SO EVEN IF IT HAD A REVERSE AND THIS WHOLE LH THREAD CUTTING THING WAS A WHOLE LOAD EASIER FOR ME I DONT THINK A CLOCKWISE CUT WOULD LOOSEN THIS CHUCK TYPE
12-21-2013, 02:43 PM #15
12-21-2013, 02:52 PM #16
Anyway, I have a Chipmaster and first question you really need to answer is, does your machine have a 3 phase motor? A lot of what you want to do is dependent on the answer to that.
If I want to reverse mine without disengaging the half nuts, I just reverse the motor, but it's a 3 phase motor and I can plug-reverse it without waiting for it to stop if I want to. My Emco single phase lathe has to come to a complete stop before I can reverse its motor but other than that the procedure is the same. Set up thread pitch & direction (RH or LH), engage half nuts, scratch shaft, check with thread pitch gauge, cut thread in multiple passes. If it's a bastard pitch (the idiotic US 1/2" UNC comes to mind) disengaging the half nuts is a bad idea so reversing the spindle is highly advisable, ditto metric on an inch leadscrew & vice-versa.
With a 10 tpi thread on a 4 tpi leadscrew you should be able to re-engage the half nuts on any even division of the thread indicator - I think. If it was a multiple of 4 you could re-engage anywhere. Funnily enough a lot of the threads I cut are multiples of the leadscrew pitch if I can manage it.
12-21-2013, 06:01 PM #17
I was not referring to the chuck on your metal working lathe. If it is a camlock chuck it is safe to run it in either direction. I was referring to the 1" BSF spindle thread on your wood lathe onto which you will screw the faceplate. If the faceplate is over the lathe bed the spindle nose thread will normally be right hand. If the faceplate is on an extension of the headstock spindle on the outer end of the spindle, a left hand thread in the faceplate is correct. Sorry for the confusion.
12-21-2013, 11:12 PM #18
On the Chipmaster, the "back gear" lever on the headstock does two things: it engages the reduction gears inside the headstock for low speed, but it also activates the end gears inside the big swinging cover on the left end of the machine. The left-most lever on the gearbox, the one that sits in a U-shaped cutout in the swinging end cover, switches between toothed belt input (lever up), and end gear input to the quick-change gearbox. The conventional way to set up for threading on the Chipmaster is the put the headstock in back gear and push the left-most lever down so that the end gears drive the leadscrew through the gearbox. However, for very fine threads, you can also thread while powering the gearbox with the toothed belt usually used for feeding. To thread this way, put the lathe in high range (i.e., don't use back gear), and leave the left-most lever up so that the toothed belt drives the gearbox. That is the purpose of the right-hand section of the gearbox threading chart; it lays out the lever positions for fine threads and feed rates. If the left-most lever is down when the lathe is in high range, no feeds or threading will work, because the end gears are not operating. On my Chippie, the left-most lever is balky, and sometimes will only shift while the gears are rotating under power. Obviously, I do this at very low spindle speed.
12-22-2013, 03:05 AM #19
I HADNT GOT ANYTHING DONE YESTERDAY BUT TODAY I WILL BEGIN SOME MORE PRACTICE THREADS UNTIL I HAVE THIS NAILED DOWN. THEN I MAY BEGIN WITH SOME YOUTUBE TUTORIALS ON THIS MACHINE AND A LOT OF THESE PROBLEMS IN ENCOUNTERING AND LIKELY MANY MORE TO FOLLOW, AS THEIR IS ABSOLUTELY NOTHING LIKE THIS ONLINE FOR THIS MACHINE.
I DO HAVE A VERY GOOD MACHINE, CAME COMPLETE WITH A COMPLETE HYDRAULIC PROFILE CUTTER/COPIER AT THE REAR OF THE MACHINE BED, NOT YET USED. THE WHOLE MACHINE IS VERY TIGHT AND TRUE ALTHOUGH I HAVE NOTICED A SLIGHT AMOUNT OF PLAY BETWEEN THE BED AND THE SADDLE, ITS ONLY NOTICEABLE WHEN MAKING CUTS AS MOVING THE SADDLE ONE DIRECTION WILL MOVE THE CUTTING TIP A VERY TINY AMOUNT AWAY FROM THE WOKPIECE AND WHEN MOVING THE OPPOSITE DIRECTION CAUSES THE CUT TIP TO DRAW INWARDS TOWARDS THE WOKPIECE. THE BED IS IN TIP TOP CONDITION AND THEIR ISNT ANY SUCH WEAR IN IT WHATSOEVER AS IVE MEASURED THIS WITH A GUAGE, TESTING FROM UP CLOSE TO THE HEADSTOCK WHERE I KNOW THE BED HASNT HAD ANY CONTACT WITH THE SADDLE IN ITS LIFE AND REFENCING THIS WITH A GUAGE AND ALSO A SRAIGHT EDGE ALONG THE WHOLE BED LOOKING FOR ANY WEAR. I GATHER THAT THE BED IS HARDENED STEEL AND THE SADDLE ISNT, SO ANY WEAR WOULD BE WITHIN THE SADDLE. GIVEN THAT I LIKE MY MACHINES TO BE SO! SO! WHEN I COME TO RESTORE THIS COMPLETE MACHINE I MAY JUST TRY TO FIND A REAL GOOD CONDITION SADDLE FROM ANOTHER CHIPPY OR THE BANTAM WHICH USES THE SAME SADDLE? OF COURSE THIS MAY JUST BE NORMAL, I DONT KNOW? COULD BE JUST WHAT THEY REFER TO AS SLOP! AS IT REALLY ISNT MUCH PLAY AT ALL. I WILL MEASURE THE COMPLETE AND WHOLE MOVMENT TODAY OF THISSADDLE AND LET YOU GUYS KNOW LATER FOR YOUR OPINIONS.
ALSO I WILL CHECK OUT THE ELECTRIC MOTOR AND HOPEFULLY SOME OF YOU CAN ADVISE ME IF I CAN POSSIBLY USE THE EARLIER MENTIONED REVERSE SWITCH UNIT I HAD PICTURED AND ALSO REFERED TO HERE
WOULD MY MOTOR ALLOW IT TO FUNCTION IN REVERSE WITH THIS KIND OF SWITCHING UNIT? I WILL NOTE MY MOTOR TYPE AND MODEL ETC LATER FOR SOME ADVICE, AS A REVERSE ON THIS MACHINE IS VIP!
Sorry For Capitols! Started typing and hadn't realised CAPS on, an im sure as hell not re-typing all that now its done.
12-22-2013, 03:13 AM #20