Warco GH 1224 screw cutting problems

[TrevorhParticipant @trevorh]

Looking for help and advice on my Warco GH 1224

I have been attempting to screw cut on my lathe, and it was disastrous, I followed the chart that is on the lathe – selected the correct gears to cut a 1.25 metric thread, treated myself to an external and internal cutting tool with the correct bit attached, set the lathe to a slow speed and put a light cut on

Engaged No 1 on the dial and away it went, stopped put the saddle back to the start and set it going again this time it cut right in the middle of the first cut….!!!

started again with the same result, then noticed a lot of back lash in the saddle and the cross slide – See Photo's in the album

Question 1 what am I doing wrong

Question 2 what can I do to get rid of the back lash

Suggestions please

Please bear in mind that I have never had to cut a thread using the lathe before in my life

The photo shows the back side of the saddle

Edited By Trevorh on 31/01/2014 09:52:23

Edited By Trevorh on 31/01/2014 10:01:05

[TrevorhParticipant @trevorh]

[TrevorhParticipant @trevorh]

I have actually removed the saddle completely off the lathe and have begun to strip it down and have found several things that do not look to clever, for example the siliconed plug – bear in mind this is how it arrived from New, I never saw it as its located on the base of the saddle

[TrevorhParticipant @trevorh]

Then there's all the dirt in the bottom of the housing

[Martin WParticipant @martinw]

Hi

All machines have a degree of backlash in the system and for this reason thread cutting etc are always approached from one direction to eliminate/minimize the effect. Just a couple of questions, (a) were you using a thread cutting dial to align the tool to the thread, (b) if so were you engaging the half nuts at the correct point as indicated on the dial. If in doubt then then pick a particular interval line on the thread dial and use this for each pass of the tool. It takes more time as one has to wait for that interval/marker to become aligned with the indicator datum mark. I assume that the half nuts were fully engaged during each pass and the control lever in the fully engaged position.

When the half nuts are fully engaged there should be little if any longitudinal free play on the saddle. If there is check for play and/or wear in the lead screw, half nuts etc and adjust so that this is all at a minimum.

Hope this helps.

Martin

PS If you have a dial indicator then there should be a table somewhere telling what interval markers can be used for each thread.

Edited By Martin W on 31/01/2014 11:02:51

[Anonymous]

Is it a metric or imperial version and have you checked the machine's manual threading section? you often find cutting metric on an imperial you ignore the dial indicator but have to leave the half nuts engaged permanently and stop/reverse at the end of each pass like a Chester DB10 I've got.

Edited By Mick Berrisford on 31/01/2014 11:18:17

[TrevorhParticipant @trevorh]

Hi Martin, thank you for your reply,

You say that the threading is from 1 direction but how do you then remove back to the start of the thread?, surely you have to wind out the cutter and then move the saddle back to the end of the bar, turn the cross slide back to the original distance and add a little to cut deeper (I assume I am suppose to take multiple cuts to get the depth correct)

Next point

Please see the photo's of the tables

My example is that I wanted a 1.25 mm pitch so according to the chart

I select M II and B 2 using the gears 22T and 45T, if I am reading it correctly will traverse and cut at 1.25

If that's not the case could you explain Please

Tonight I will clean and check the setting of the half nuts but I need to clean the whole unit first and replace some Chinese fittings for something more reliable

 

cheers

Edited By Trevorh on 31/01/2014 11:27:40

[TrevorhParticipant @trevorh]

Hi Mick,

good question, I don't know but it came with the gears to cut both and as you can see from the chart it does list both, I did wonder about keeping the Half nuts closed and just stopping and reversing back to the front but that comes back to my initial point that due to the backlash in the saddle it still kept damaging the first cut

It could be possible that I do need to reset the half nuts but that will not address the play in all of the saddle gearing – I mean it really is a lot of play (shake rattle and roll type play)

Please see the other photo's in my album

cheers

Edited By Trevorh on 31/01/2014 11:42:54

[Martin WParticipant @martinw]

Hi

First of all I notice that you have a 127 gear listed in the change gears and this gives you a direct conversion for cutting in either metric or imperial pitches (5 x 25.4 = 127) so there is, unlike some smaller machines including mine, no approximation on thread pitches.

To cut a thread, using the longer method, back the saddle to the right until the tool is clear of the work piece. Set the depth of the first pass cut using the cross slide and if you can lock the cross slide; again make sure that for each pass you advance the cross slide thereby moving the tool into the cut so as to eliminate the backlash.

With the half nuts disengaged and the thread indicator engaged move the saddle, by hand, until a particular index marker on the thread indicator aligns with the datum mark. Close the half nuts if they won't close select another marker and repeat. It may be that you will need to adjust the reference point until this happens. LEAVE THE THREAD INDICATOR ENGAGED FROM NOW ON.

Start the lathe and the saddle should start to traverse taking the tool to the work piece. The thread indicator should not rotate at this stage. At the end of the cut stop the machine, withdraw the tool, remembering the cut depth on that pass, disengage that half nuts and wind the carriage/saddle back to its approximate starting position. During this the thread indicator dial will rotate.

Move the carriage until the same marker on the thread indicator dial aligns with the datum mark, ensure the tool is beyond the end of the work piece. Wind the tool in to a depth that is the last cut setting plus the next cut depth. Engage the half nuts, these should engage readily and the thread dial indicator should not change. Start the machine and repeat the process until you have the desired cut depth.

You can cut threads in many ways and I have used the above method successfully as it is a useful starting point. If the machine has an easy reverse function then this can be used and the half nuts left engaged all of the time, the saddle is returned to its starting point by stopping and then reversing the motor until it is wound back to its starting position and the process repeated.

Hope this ramble helps a bit will look at the dial gauge table and see if I can help with that but I expect more experienced users on this forum will be posting.

Have fun

Martin

PS

It is useful to have a small recess, just smaller the root diameter of the thread, at the end point of the thread which allows the tool to finish in a free area. Without iy one can easily over run the previous cut/s with disastrous results, don't ask how I know . 

PPS

It looks as if you have a lead screw reversing facility on this lathe. Do Not use this to return the carriage/saddle to its original position if you are going to use the continuous engagement of the half nut method as this will destroy the registration of the lead screw to the chuck spindle.

Edited By Martin W on 31/01/2014 12:42:37

Edited By Martin W on 31/01/2014 13:13:23

[BazyleParticipant @bazyle]

"Play in the saddle gearing" doesn't matter one jot for threading. Do you know there are two methods of making the saddle move and there is a lever or dial to select between them. "screwcutting" and "feed".

For threading you use the lever at the right of the saddle that engages the half nuts direct on the leadscrew – no gears involved but there will be some play in the fit of the half nuts to the screw. This does not matter at all – my elderly Boxford has nearly 1/8 in backlash. So for a beginner you have to reverse the lathe keeping the half nuts closed until you get back beyond the start of the thread. Then start forward again to take up the slack before the cut starts. You will have to provide clearance for this if the thread is not at the end of the work.

The other option "feed" uses the rod below the leadscrew to turn the gears to turn the handwheel to engage with the rack under the bed edge to pull the saddle along. This is not for screwcutting it is just to save lazy operators from winding the handle.
On your lathe the top two tables are these feeds "0/mm" and "0/inch".

There is an interlock to prevent both methods of movement being engaged at the same time.

[TrevorhParticipant @trevorh]

Many thanks Martin, Bazyle,

That's excellent information for me

1. Martin, Once I have re assembled the saddle I will experiment with how you have described, actually sounds logical

2. Bazyle, Thanks for that, I hadn't understood what was doing what when screw cutting so that again makes sense, and it is actually as you have stated

Its looking at least that its me and not the equipment, which is somewhat of a relief, because at least I can learn by my mistakes

Cheers

[Thor 🇳🇴Participant @thor]

Hi Trevorh,

hope you manage to sort out the backlash problem. From the pictures you posted it seems you have a lathe with an imperial leadscrew. The threading dial table shows threads per inch and how to use when cutting imperial threads. I don't think you can use the threading indicator for an imperial machine when cutting metric threads – even if you hav a 127T gear. You should follow Mick's advice and keep the half nuts engaged while cutting metric threads.

Thor

[Jerry WrayParticipant @jerrywray14030]

Hi Trevorh, and Thor,

I took delivery of a new Warco GH1322 metric lathe a few weeks before Christmas. I was flummoxed by the thread dial at first but reading the related Grizzly manual was very useful to me. I have not read the Grizzly manual for your machine, which may well be different.

My thread dial has facilities to engage in 3 different positions dependent on which leadscrew and gear configuration is provided. The machine is also equipped with a 127T gear which only appeared after I had turned upside down the kit which came with it.

The Grizzly relevant manual makes all the difference.

Jerry

[TrevorhParticipant @trevorh]

thank you for all of the support and answers

I will be rebuilding the saddle over the weekend and have downloaded a copy of the manual

Shall be experimenting next week so will keep you all posted on the outcome

cheers

[John Stevenson 1Participant @johnstevenson1]

Buy the book Screwcutting in the lathe by Martin Cleeve.

You wouldn't jump into a car and try to drive it without lessons would you ?

[TrevorhParticipant @trevorh]

Hi John,

If the book had any relavance to the controls and methods required to screw cut on my particular model lathe then of course I would have purchased a copy but as it has very little information that would be useful in this situation I didn't bother

Its better to understand the controls first then understand the operation you perform

Before you take a driving lesson you are taught what the controls are first.

[Les Jones 1Participant @lesjones1]

Hi Trevorh,
I do not believe there is a fault with your lathe. I think the problem is that you do not understand that to be able to disengage and re engage the half nut the thread you are cutting must repeat in such a way that if you move along it by the pitch of the leadscrew then you will be an INTEGRAL number of the threads you are cutting from when it was disengaged. So if you have an 8 tpi leadscrew and are cutting an 20 tpi thread then if you move one thread along the leadscrew you would start cutting on the crest of the thread. I think this is the point John is making. In a way the fancy gearbox on your lathe is not a help to start with. If you had just bought a lathe with a box of gears and given the pitch of the leadscrew it would force you to understand the screwcutting process rather than doing it cookbook fashion from the charts.

Les.

Edited By Les Jones 1 on 01/02/2014 10:01:15

[John Stevenson 1Participant @johnstevenson1]

Posted by Trevorh on 01/02/2014 09:11:44:

Hi John,

If the book had any relavance to the controls and methods required to screw cut on my particular model lathe then of course I would have purchased a copy but as it has very little information that would be useful in this situation I didn't bother

Its better to understand the controls first then understand the operation you perform

Before you take a driving lesson you are taught what the controls are first.

The point was if your car started juddering because you didn't know how to drive it would you take the gearbox out ?

[TrevorhParticipant @trevorh]

Well Just reporting back

Success on the screw cutting front, I rebuilt the saddle giving it a much needed oil change, cleaned up the various gibbs and slide ways, Opened up the lubrication oil ways that were completely blocked by what appears to be sand, Changed all of the Chinese screws,caps and grub screws for standard European ones and finally removed the some of the backlash in the moving parts

Read the Grizzly manual and applied the comments already received

Guess what – First attempt managed to cut a nice M12, then an M10 and M6

On this particular lathe the Half nut must be kept engaged when cutting metric threads but is dis engaged when cutting imperial threads as per the advise given

Now that I know the VERY basics I am happy to invest in a book to learn the intricacies of threading

Many many thanks to those who posted

[Martin WParticipant @martinw]

Hi Trevorh

Glad to hear that you have managed to cut some threads and in the process have given you lathe a bit of a service. This never hurts and certainly helps one understand the strengths and weaknesses of a machine.

Have fun and don't get too screwed up if you turn your crests into valleys on the way .

Regards

Martin

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