Workaround for low tailstock?

[Crow667]

Hi,

I have an old beat up looking Unimat 3 that I picked up cheap a few years ago. The tailstock is not adjustable and sits slightly low.

Hasn't been a problem for most part, but now I need to make some small hollow shafts with 3-4 mm center holes through them. The drill bits when mounted in tailstock are off center and act more like boring bars, and the small ones simply break.

I don't have an individually adjustable chuck, and the way the chucks (drill, 3 jaw and self centering 4 jaw) screw on tailstock, they tighten down at odd angles (so I can't just put a single shim between the drill bit and lower chuck jaw).

Are there any other macgyver style tricks to get the drill bits centered?

Edit: might have found a way. Put 3 jaw with drill bit on headstock, drill chuck on tailstock, took the cheapest shittiest chinese 1/4 screwdriver bit I could find and put it backwards into drill chuck, then drilled about 10mm into its base. Removed drill bit from chuck and inserted it tail first into drilled out screwdriver bit.

Now just have to find a way to fix it, don't have any adhesive besides common superglue left, and all hardware stores here are closed due to covid...

 

[goldstar31]

Just off topic but are you sure that the fault is not 'worn round bed bars? Rex Tingey replaced his years ago.
His book, in case you do not know, is Making the Most of the Unimat.
In extremis, consider scraping the spindle end.

Regards

Norman

 

[Crow667]

It's a mk3 with conventional cast bed. I suppose it should be possible to work out what exactly is wrong there by turning a couple of cylindrical workpieces of different length between centers, then carefully measuring them and tabulating the results?

 

[goldstar31]

Apologies, I was thinking of the older SL. I had a SL and the a clone of a 3/4 which was a MJ-189

 

[BaronJ]

Hi Crow,

Sounds silly but try a slip of paper under the tailstock. Copy paper is about 5 thou and the non stick paper that you peel labels from are 2 thou. It wont last forever but will get you out of trouble.

 

[oldengineguy]

Not silly at all BaronJ! I have an old worn SB Heavy 10 and have put a strip of 003 shim stock under the flat side to bring the tail stock up to very close to where it should be . When I drill a small hole it is really close to what it is intended to be. Centre side to side after you shim. Colin

 

[nautilus29]

Like baron said shimming is probably your best option. Especially since you could have an issue with your ways and even if you found the perfect height at one spot on your bed, it might not be perfect at another.

If you did do some testing and found that your bed is reasonably flat, and the issue is with your tailstock. You could machine some material off the bottom of the tailstock and make a shim to raise it back up. For example machine 1\8 off the bottom and make a shim that raises it back up to true height.

 

[IanN]

It's a mk3 with conventional cast bed. I suppose it should be possible to work out what exactly is wrong there by turning a couple of cylindrical workpieces of different length between centers, then carefully measuring them and tabulating the results?

Hi “Crow”

As Norman and yourself point out, any attempt to cure the problem without knowing what the problem is will have you running round in circles - correcting one problem simply introduces another

There is a well established sequence to follow to check and align a lathe.

DO NOT use Rollie’s Dad’s Method (often referred to as RDM). It is fundamentally flawed as it makes some assumptions which may not be true - remember one of the golden rules of engineering “Assume nothing, check everything”

The sequence to check/true a lathe:

1) Using a flat reference (surface plate or well supported sheet of plate glass) check the bed is flat and true (not bowed or skewed) - Correct if necessary

2) Using the bed as a reference and a DI or DTI check the headstock spindle axis is parallel to the bed ways both vertically (“dip”) and horizontally (side to side across the axis) - correct if necessary

3) Using the headstock spindle axis as a reference, check the tailstock ram/spindle is parallel with the headstock axis in the horizontal (side-to-side) plane by comparing readings with the ram fully retracted and fully extended - correct if necessary

4) Repeat step 3, testing for parallelism in the vertical plane - correct if necessary

5) Using the headstock axis as a reference, check the vertical displacement of the tailstock axis with respect to the headstock axis - correct if necessary

6) Repeat step 5, testing axis displacement in the horizontal plane - correct if necessary. The headstock and tailstock are now co-axial

When using the lathe, the headstock axis is the system reference. You now have a flat, true lathe bed accurately aligned with the headstock axis and a tailstock ram accurately co-axial with the headstock axis

The final steps are to check the motion of the cross slide is perpendicular to the spindle axis (aim to have the cross slide turn a very shallow dish) and the head- and tailstock tapers are co-axial with their respective spindle axes

Notice that the process is linear - there are no loops to go round dealing with two adjustments that interact

I you miss any of these steps (or do them in the wrong order), you may solve a problem for one setting of the tailstock, but you will introduce errors at other settings

Finally, all things are relative, and an acceptable level of accuracy depends on what you intended to do with your lathe....


Whatever you do, just make sure you have fun!
All the best,
Ian

 

[goldstar31]

Following on from our erudite experts, I was wondering how you established how your tailstock was too low. Surely, you didn't simply stick a pair of centres into the spindle and the tailstock-- and simply push the tailstock up so that the centres met-- and discovered what you believed was that the tailstock was OUT?

If you recall, I wrongly mistook the SL for the Mk3/4. I suggested wear in the bed bars.

So before any 'remeial work' that you clarifies YOUR technique. It may not be the correct method which others have adopted over many years

 

[Crow667]

Sorta kinda like that, with tightly fitting fixed centres and a thin feeler gauge between them to check slant. Spinning the spindle had very little (but still slightly noticeable) effect on it. Tried it with ram extended to various degree so the tailstock would sit on different points on the bed, stayed roughly the same.

Also turned a few 5 or so inch shafts a while ago (between centers) and they came out slightly conical, dont remember exactly by how much.

I absolutely AM a complete n00b btw and learning as I go...

 

[goldstar31]

As I guessed, your lathe bed shears and not your tailstock are worn near the spindle.

This causes the 'drop'.
The remedies are many and various and perhaps using packing as suggested by John B may be the easiest 'work round for you.

Ut's a common complaint in bigger lathes at about 6 inches from the headstock
Best Wishes

Norman

 

[Chiptosser]

Crow, The first thing I would look at is: does the drill chuck shank have any nicks or dings in it? Have you blued the shank to see if there are any dings or marking from inside the quill? That would be the first order of business if not already addressed.

 

[Crow667]

Ok

Tested the chucks. The 3 jaw is ok. The 4 jaw is pretty bad. The drill chuck looks like its ******* done. Epic runout, and the lathe came with both a milling head (with a table and fine down adjustment and all), no collets, and a bunch of rusty mill bits in a ziplock bag.

Will test it seriously wheneber I can secure a reliable source of O rings aka drive belts (it goes through them like **** through goose, I've got only 2 left, and like I said, covid shutdown).

Thx for help, and please feel free to "insult my intelligence" anytime. Like I said, a total noob here.

 

[Richard Hed]

Hi,

I have an old beat up looking Unimat 3 that I picked up cheap a few years ago. The tailstock is not adjustable and sits slightly low.

Hasn't been a problem for most part, but now I need to make some small hollow shafts with 3-4 mm center holes through them. The drill bits when mounted in tailstock are off center and act more like boring bars, and the small ones simply break.

I don't have an individually adjustable chuck, and the way the chucks (drill, 3 jaw and self centering 4 jaw) screw on tailstock, they tighten down at odd angles (so I can't just put a single shim between the drill bit and lower chuck jaw).

Are there any other macgyver style tricks to get the drill bits centered?

Edit: might have found a way. Put 3 jaw with drill bit on headstock, drill chuck on tailstock, took the cheapest shittiest chinese 1/4 screwdriver bit I could find and put it backwards into drill chuck, then drilled about 10mm into its base. Removed drill bit from chuck and inserted it tail first into drilled out screwdriver bit.

Now just have to find a way to fix it, don't have any adhesive besides common superglue left, and all hardware stores here are closed due to covid...

A more permanent method might be to shim the tailstock. Doesn't the tailstock have an adjusting plane for making bevels? You should be able to shim it there.

I once had to work with a Monarch that had 20thou out abut 6-12" from the spindle nose. I had to make accurate parts with this and that was not always easy.

 

[Crow667]

A more permanent method might be to shim the tailstock. Doesn't the tailstock have an adjusting plane for making bevels? You should be able to shim it there.

Absolutely not. It's a toy looking one piece affair.

The lathe came with an almost broken aluminum fixed steady that I finally managed to break, and the replacements on ebay cost about half of what I paid for the whole set. Made one out of PETG on my chinese prusa knockoff 3d printer, and it works just fine.

Prices for those things on ebay are absolutely nuts, I could probably sell it and buy an actual lathe for the money... If I had a place to keep it.

 

[Richard Hed]

Absolutely not. It's a toy looking one piece affair.

The lathe came with an almost broken aluminum fixed steady that I finally managed to break, and the replacements on ebay cost about half of what I paid for the whole set. Made one out of PETG on my chinese prusa knockoff 3d printer, and it works just fine.

Prices for those things on ebay are absolutely nuts, I could probably sell it and buy an actual lathe for the money... If I had a place to keep it.

I am not really; familiar with this. Could you send a photo? Certainly you could find room to put a real lathe. I recommend kikking the wife out of bed and putting it there. She can sleep on the couch or in the dog house. I did that with my lathe but it crushed the bed so I had to put it in the garage. The wife still sleeps outside in the dog house with the dog.

On cold nights, below -30F, I let her and the dog in the house to sleep on the rug. Don't worry about fleas, we shampoo them regularly which kills the fleas. Makes one wonder what the hell is in that shampoo and whether we should be putting it on our heads.

 

[Drawfiler]

if you want a crude but simple temporary solution try this, get a blank taper arbour and put it into the tailstock, mark the top of the arbour so you can put it back in the same position. fit a centre drill to the headstock then drill and tap the arbour in the tailstock to take a screw in drill chuck.
when you use the chuck always fit it in with the mark you made to the top.
This is a real lash up but it works until you sort out;the underlying problem.
if the arbour is too small to take the thread, you can turn down the drill chuck shank by putting a small bar in the headstock, turning it true, gripping it with the drill chuck and then turning the thread down.
i:emphasise that this is a get around not a solution.

 

[ajoeiam]

Hi “Crow”

As Norman and yourself point out, any attempt to cure the problem without knowing what the problem is will have you running round in circles - correcting one problem simply introduces another

There is a well established sequence to follow to check and align a lathe.

DO NOT use Rollie’s Dad’s Method (often referred to as RDM). It is fundamentally flawed as it makes some assumptions which may not be true - remember one of the golden rules of engineering “Assume nothing, check everything”

The sequence to check/true a lathe:

1) Using a flat reference (surface plate or well supported sheet of plate glass) check the bed is flat and true (not bowed or skewed) - Correct if necessary
snip

Finally, all things are relative, and an acceptable level of accuracy depends on what you intended to do with your lathe....
snip

You might wish to be aware that on high precision LARGE equipment a deliberate crown in placed in the bed so that when a very large load is held that the weight of the items causes the bed to now be 'straight'.

(There are 2 companies that I read of doing such - - - their names presently escape me. The beds are scraped not ground - - - again, IIRC they were working to single digit micron cubic accuracy over distances of 10s of meters and expecting loads of over 10 mega grams.)

 

[napoleonb]

Besides shimming the tailstock a simple way to achieve your parts-goal is to mount the drill(s) in the toolpost. That way you can adjust height and drill straight dead centre. Search for drill chuck tool post and a lot will come up.

Just saw your tailstock in half (horizontally). Mill pockets like this |=| in the lower part and just | | in the top part. Use thick stock material in the front and back part so it is adjustable side to side and mill/grind the stock material to adjust the height.