Problem- Question about play of the wheel on the compound slide

[yang_cnc]

Hi:

Today I noticed something, which is somehow frustrating.

1. I found that the HF 7x12 is not a rigid machine. Well, I do not expect it rigid, but I found the compound slide and the cross slide all have some plays(I may not use the right term). For example, if I try to list one end of the slide, I can clearly see a very small gap open between the slide and its base.

I assume that the above is normal, anyway, the rotation work will push everything down, so the gaps(if any) will be consistent and will not move around.

2. but one thing, I definitely hate, is that I found the compound wheel(the upper most wheel) have a lot of play. Say if I turn it forward(clockwise), then I turn it backward(counter-clockwise), I can see the play as large as 8 marks(or 0.001" * 8 say 0.008").

I tried to adjust the gib to fix this(is this the right way> Anyway, except the three gib screws, I do not feel there is other stuff I can tune). But it is not easy, either it makes the slide to tight, or too loose.

Could anyone tell me whether those plays I observe are normal? especially the later one, play of the wheel.

thank you!

[yang_cnc]

Sorry, the right word is "backslash", I just forgot it. I mean there is about 0.008" backslash on my compound slide.

[Fast01]

If you go to mini-lathe.com there are complete instruction on how to adjust the backlash on the mini lathes. You can also go to littlemachineshop.com, they have a .pdf you can download with complete instructions on setting up these lathes as well. That's the one I used. Although I think the information is from the same source.

[escott76]

Originally Posted by yang_cnc Hi: Today I noticed something, which is somehow frustrating. 1. I found that the HF 7x12 is not a rigid machine. Well, I do not expect it rigid, but I found the compound slide and the cross slide all have some plays(I may not use the right term). For example, if I try to list one end of the slide, I can clearly see a very small gap open between the slide and its base. I assume that the above is normal, anyway, the rotation work will push everything down, so the gaps(if any) will be consistent and will not move around. 2. but one thing, I definitely hate, is that I found the compound wheel(the upper most wheel) have a lot of play. Say if I turn it forward(clockwise), then I turn it backward(counter-clockwise), I can see the play as large as 8 marks(or 0.001" * 8 say 0.008"). I tried to adjust the gib to fix this(is this the right way> Anyway, except the three gib screws, I do not feel there is other stuff I can tune). But it is not easy, either it makes the slide to tight, or too loose. Could anyone tell me whether those plays I observe are normal? especially the later one, play of the wheel. thank you!

Backlash can be a "fact of life" in machines like this. Using machines like this, you must always take your measurement turning the screw the same way, and if you do have to reverse it, making sure you turn past the backlash.
Always approach the desired number by turning the screw in the same direction. Although you can adjust out *some* of the lash by adjusting the nut, wear will bring it back. In lathe work, to get correct fits in bearings, and bores, you will need to cut, stop the lathe, measure the part, adjust, take another cut, repeat. A good micrometer helps here too. Get some stock and a mic, and practice turning to a specific diameter, + or - .005 to start. Don't rely on a digital caliper for measurement of this either, it's not going to do what you want it to.

[yang_cnc]

Originally Posted by Fast01 If you go to mini-lathe.com there are complete instruction on how to adjust the backlash on the mini lathes. You can also go to littlemachineshop.com, they have a .pdf you can download with complete instructions on setting up these lathes as well. That's the one I used. Although I think the information is from the same source.

yes, i carefully read it. it does provide a lot of helpful tuning info, unfortunately, the author did not mention backslash happened to the compound wheel (leadscrew).

One more thing interesting, if I am right, I believe there is some mistake on the wheel of my HF lathe. It is marked as each graduation is 0.001" or 0.025mm. Each wheel has 80 graduations, so it represent 0.08" or 2mm per whole turn of wheel. But, actually, I turn the wheel 10 turns, I only see about 10mm travel(just half of it should be 2mm x 10 = 20mm). So the marking is not right at all. It is still the old HF lathe of 40 graduations, but per graduation is 0.001". My lathe just divides each graduation into 2 to get smaller division.

[ibuildstuff4u]

The wheel is correct, it's because you remove twice the amount of material than what you dial into the compound. When you take off .001 you actually remove .002 because you are taking material off both sides of the part.

It makes it easier to use the lathe when you have a dial that reads the true amount that is going to be removed rather than the actual movement of the tool.

Dale P.

[yang_cnc]

en, this explanation makes sense...

[wildwestpat]

Originally Posted by yang_cnc yes, i carefully read it. it does provide a lot of helpful tuning info, unfortunately, the author did not mention backslash happened to the compound wheel (leadscrew.) ................

Hi

The lead screw in the compound slide runs in a thread cut in the other half of the dovetail slide mounted on the cross slide and is not adjustable unlike the cross slide which has a rocking screw type of adjuster to get the nut lined up with the screw and a little bit of pressure (vertical twist) to reduce any backlash. The thrust arrangements may vary from make to make and are a bit crude. Just slacken the handweel retaining nut and undo the handle a bit - grease the surfaces of the compound slide bearing face - the 'calibrated thick washer cum dial. These on my lathe are ground smooth and form the thrust bearing for the lead screw. Retighten the handle and stop when you have just sufficent pressure to give a nice action. Locking the handle lock nut will alter the feel and you will have to adjust to get a satisfactory feel against minimal backlash.

Others have mentioned how to cope with backlash when machining i.e. allways make the cut withdraw the tool and start cutting again by turning the screw in the same direction as for the previous cut. This method applies to even the more exotic lathes if the best tolerances are to be achieved out of the respective machines.

As to the dove tail gaps you might like to check that the gib is in the right way up. I had a similar concern and found mine had been inserted the wrong way. The dimples in the gib line up with the screw points and help force the slide down onto the ground seating area by holding the gib steady.

Hope you become happy with your lathe as it is capable of some good work given the odd tweak.

Regards

Pat

[yang_cnc]

Pat:

I very appreciate your nice explanation of methods you employed.

But I have several places I do not quite get you, I quote your post here:

"The thrust arrangements may vary from make to make and are a bit crude. Just slacken the handweel retaining nut and undo the handle a bit - grease the surfaces of the compound slide bearing face - the 'calibrated thick washer cum dial. These on my lathe are ground smooth and form the thrust bearing for the lead screw."

Is the "handwheel retaining nut" is the "lock nut" you mentioned later one?

By "thrust arrangemnt", I guess you mean those parts on the handwhell, handling the thrust force along the axis?

"calibrated thick washer cum dial', I have no idea what it is. Is it the wheel on which there are some graduations?

I am thinking adding some spring to the slides and its dovetail base, such that it can compensate the backslask. Actually, if I use my fingers to exert some force on the slide to a direction, then I feel the backslash is gone no matter which direction I am turning.

But this project, currently, may be beyond my shills...

Thank you and have a good day!

[wildwestpat]

Sorry I did not make myself clear:-

I very appreciate your nice explanation of methods you employed.



Q1 Is the "handwheel retaining nut" is the "lock nut" you mentioned later one?

A1 Yes the handweel on some is a ball and lever type of knob - both types are threaded and locked onto the lead screw with a lock nut.

Q2 By "thrust arrangemnt", I guess you mean those parts on the handwhell, handling the thrust force along the axis?

A2 This is where the arrangements may differ and what I was trying to explain is that the end of the casting that provides the dove tail housing and the tool post mount is machined square with the lead screw thread. Against this machined end there is a drum that has the index mark. This drum / cylinder is held onto the compound slide by two screws. The surface of the 'drum' and the end of the slide should be clean and the screws reasonably tight.

Q3 "calibrated thick washer cum dial', I have no idea what it is. Is it the wheel on which there are some graduations?

A3 Yes. This dial drum forms one side of the thrust arrangement with the other face being the drum that has the index mark. When the hand weel / handle is slackend off by undoing the lock nut then the handle the two 'drums can bbe separated. Check that these surfaces are smooth and lightly grease or use thick oil. Re tighten the hand wheel and lock nut by trial and error until you have an acceptable backlash and are still able to turn the leadscrew easily. There is a tendancy to leave the adjustment with too much clearance - the wheel should require a little bit of force to turn it.

The 'force' required is also adjusted by the gibs and until you have experienced the correct set up of both the gib screws and the leadscrew thrust arrangement it is difficult to describe. I have just been and looked at my lathe and it takes between 4 and 8 oz inch to turn the compound lead screw.


I do not think adding springs will help as this will only store energy which will increase any tendancy for the tool to chatter. Normally the backlash in the leadscrews on a lather are of little concern if the gibs are sufficiently tight because the tool is always being advanced in the same direction. That means that the slop i.e. backlash has already been taken up in pushing the tool to advance the cut.

The backlash does become a concern with some more exotic configurations but there is almost invariably a way out of the problem.

You are learning fast so your skills will be improving and the backlash demon will soon be gone if you adjust the cross slide and the compound gibs as I have described. This will give you a reasonably stiff tool post mount which also ensures the backlash that remains is accounted for as the tool is advanced into the work. {Remember the tool cutting force is acting to keep the screw engaged in the same direction - if you add a spring it has to work to push the tool away from the cutting edge or have a force that is much higher than the cutting forces. This is in my opinion difficult to arrange without major alterations to the lathe.}

I suggest you leave the sadle gibs alone for the time being as these are less easy to adjust and concentrate on getting the compound and cross slides working properly.

Sorry to keep on about the backlash is no problem but I feel it is necessary to get you cutting metal when I think the theoretical niceties will fade away as you start producing accurate work. If you with draw the tool from the cut do so by an amount that far exceeds the total backlash and wind in again so that by approaching each cut from the same direction accuracy is maintained. This is good workshop practice any way and will help you if or when you start with CNC.

Hope this clarifies the adjustment and the reasoning. If not ask again.

Regards

Pat