Member postings for Huub

Start by adjusting the gibs. Once these are OK, you can judge the "state of the ways".

Loosen the gib adjusting screws a full turn. Now the table should move smoothly without drag.
Just by using your finger tips, slightly tighten the adjusting screws without applying any torque.
The table should still move smoothly without drag.
Try to move the table over its full length. You may find it will take more "force" on the end due to wear and asymmetrical weight (table not in balance).

If this doesn't help, remove the gibs, clean and oil the ways and try again.

Under CNC control, taking a 0.005 mm cut in aluminium using a CCGT060204 insert (uncoated, ground) is not a problem (do this on a daily base) even on the mini lathe. In aluminium, I could cut as shallow as 0.002 mm (stepper resolution).
For steel I would use the same CCGT060204 insert insert but the 0.005 mm depth of cut would be the limit.

The biggest problem is measuring the diameter, not the turning part. For inside diameters my 2 point gauges are just not repeatable enough. That is not a gauge issue but more my ability to position the gauge the right way with the part in the chuck. Measuring a calibration ring with ground surfaces is not a problem.

Grinding the tip of an end mill is not that difficult. Put the end mill in a hex collet, set the mill on a 3° angle and grind the flutes with a (dremel) diamond disk (0.1 $ on ebay). They will be as new.
If you grind them often (like me), they won't be usable to plunge a hole but that is a minor.

Once a year, I grind my end mills, drills, slitting saws, roughing end mills on the CNC (mini) lathe with a Dremel in the tool post.
You have to cover all other machines with blankets and still have to clean the ways from all machines to get that HSS dust away. So after grinding, all my machines get their annual maintenance.

I only grind HSS tools (HSS M2). I don't grind tools that contain cobalt because cobalt dust is toxic.

I don't think this light weight lathe can use a/one ground form tool to turn the shape of the belt. It is just not ridged enough for such a large cutting edge.

I have seen Youtube video's (one of our dutch members also has done it this way) where the required shape is turned in brass using the method used by wood turning. A sharp tool, a tool rest and turning the shape by hand.
Free hand lathe turning

Another way is this way:
Free form lathe turning

Edited By Huub on 23/06/2023 22:19:39

A milling machine, standing in the garden (for some time) in working order that can't be tested, is a gamble. Such a heavy machine isn't a walk in the park to take apart.

Here in the Netherlands, these type of machines are for sale quit often so I can wait for a machine that can be tested.

From Mitsubishi I use the DCMT070204 VP15TF inserts for steel. These are intended for finishing. DCMT070202 inserts have a smaller nose radius and will need less cutting forces. These inserts are also sharp enough for turning POM or brass.

For aluminium I use the uncoated ground inserts from Korloy DCGT070204 AK H01. These are also available as DCGT070202. These work also for POM and steel because the cutting forces are low due to the very sharp ground cutting edges.

I use a different style of QCTP for some years now on my lathes. It requires to adjust the tools to fit the tool post but that is a one time procedure. It is "cheap and easy to make" and it doesn't compromise the rigidity of the lathe. It allows for very repeatable (better than 0.02 mm (3S value, 99%) in turning diameter) repositioning of the tools.

I have uploaded an incomplete not edited video of the old design that will show how it works. The new design doesn't require rotating the top plate when changing from inner to outer turning. As soon as I have the time, I will upload a new video.

QCTP video

Edited By Huub on 17/06/2023 22:16:55

Ian,

Good to hear you have things working for you.

I have checked the minimum turning diameter for my 12 mm boring bar (S12M SCLCR06, CCMT060204 insert) and that is 13 mm.

Regards,

Huub

From roughing (drilling) to finishing (turning) it takes 3 passes at an equal cutting depth if the setup (not a rigid lathe, large tool stick out, large thin stock stick out) is not rigid. Getting a decent finish under these conditions is always a challenge. You have to reduce the cutting forces to succeed. Reducing the feed/rev, depth of cut and to some degree, the RPM is the only thing you can do.
The insert is also important if you can't run under the conditions advised by the manufacturer. In general, I use finishing inserts on my not rigid desktop lathes. Large (DCMT11xxxx, WNMG08xxxx, etc) inserts are generally made for heavy turning conditions. Small inserts perform better under light cutting conditions.
I have 3 boxes of TCMT110204 VT15TF of the same brand and supplier and 3 boxes of other brands and suppliers. One of the 3 boxes gives an outstanding finish, a lot better than the other 2 boxes and the best of all 6 boxes of this insert type I have. So I use this box only for making gear gutters. All my inserts are from web shops and even the branded are probably counter fait. Never the less, 8 of 10 boxes perform well for my hobby use.
When nothing works, I use a CCGT060204 H01 (alluminum) insert to do the job.
I use 0.4 and 0.8 mm tool nose radius but I am going to test a 0.02 mm tool nose radius because I think these will do a better job (lower cutting forces) on my lathes.
You could also try a HSS tool, that should also give a good finish under light cutting conditions.

Have you thought of using a reamer. It is hard to match their finish using turning. I only have H7 reamers (+0.02 mm) but there are reamers for press fit holes.

You don't need a press fit for a bearing. You can also glue the bearing using lock tide.

Hopper,

You are right to check if the boring bar is small enough. I mark the "critical sides of the boring bar" with a sharpy and check if the boring bar doesn't contact the hole.

I have a 12 mm boring bar (S12M SCLCR06, CCMT060204 insert) that fits a 14 mm hole.

The CCMT0602xx boring bars are the "smallest". For larger diameter holes, I prefer the DCMT0702xx inserts in a Q style holder because chips don't build up so easy on Q type insert holders.

If you get 0.03 mm narrowing when using the top slide, then you have to check the alignment of the top slide.

• Put a thick bar in the chuck.
• Mount an indicator on the bar using a magnetic holder.
• Set the indicator on a point of the moving part of the top slide and zero the dial (or note the value). Mark the position of the indicator on the moving part of the top slide.
• Feed the top slide 50 mm and use the carriage to reposition the indicator at the marked position. The indicator will now show the alignment of the top slide.

If you can hold a 65 mm bar in the 3 jaw, your lathe and tool post are probably rigid enough to hold a long boring bar.

Putting a stepper on the lead screw solved the gear switching on the mini lathe. My bigger lathe has besides the change gears, a 2 and 3 position lever to select 6 different feeds.

If it need to be accurate, I use the CNC to turn an opposite taper. That requires 3 finish passes and 2 thickness measurements. That is a lot easier and faster than setting up the alignment.
For accurate drilling you still need an aligned setup.

High speed contact angle bearings are pretty expensive and requires very accurate machining. That is beyond the capabilities of me and my lathe.

Edited By Huub on 15/06/2023 18:48:51

The 45 mm long part has a 2 mm wall thickness. That results in a lot of flex especially when turning the inner diameter. Not an easy part to make!

If possible, I would turn the inner diameter first and mount the part in a 4 jaw chuck (no part stick out) to reduce the flex of the part. Bore the hole 15 mm thick and finish using a 12 mm inner turning bar. Let the inner turning bar stick out 47 mm max. Select a feed/rev as slow as possible. On my mini lathe in manual mode, that is 0.1 mm/rev. Bring the stock to final diameter using a cutting depth of 0.05 mm or even less. A sharp insert (for alluminum) should work fine.
If there is chatter, reduce the RPM and cutting depth if possible.

On my mini lathe, I only have a 3 jaw chuck that has a 16 mm bore. So the part would stick out quit a lot. I would follow the same procedure but turn CNC at a feed of 0.02..0.05 mm/rev.

Another cause for the bump in the measurements could be some "damage" on the trapezial part ( single prismatic feature) of the lathe bed. If something drops on this part, it will cause a dent and also high spots near the dent. You can grind away these high spots using a small stone.

You are right, static measuring and actually turning can/will give different results.

I prefer making a " Rollies Dads" test bar because it is easy and cheap to make and because it is running true it makes adjusting a lot easier.

The bump in the measurements could indicate wear (not worn) of the lathe bed. It can also indicate that the gibs are to tight or a combination of both.
Measure once moving the carriage from left to right and once moving from right to left. If you find similar results, the gibs are not to tight.

20 microns/100 mm isn't bad for a "stock" mini lathe. Beware, it would mean 0.04 mm in turned diameter. If you are happy with these results, than all is OK.

If you have a chuck mounted, the first 40 mm of the lathe bed aren't used. So it is to be expected that this part of the lathe bed is in mint condition.

This is how I measure the headstock alignment with the chuck in place:
Measuring headstock alignment

Edited By Huub on 12/06/2023 19:10:04

You can measure the tilt using an indicator but you probably feel the headstock/saddle/tail stock rocking when pressing on one of the four corners. Weep off any oil because that influences the measurement.

You have to check the tilt of the headstock at its mounting position.
You can check the tilt of the saddle/tail stock on any position of the bed. I used the end of the bed because that is worn the least.

The hardest part to get right is the head stock alignment. Once the head stock isn't rocking any more, you can adjust the alignment. For that you have to remove metal on two places so the headstock doesn't start rocking again.
For changing the up/down angle, you have to remove metal on the front or the back (flat side and both sides of the V).
For changing the left/right angle, you have to remove metal on 2 opposite sides of the V.

Because you don't remove much metal, It is a slow process so it takes a lot of trials to see a change in the alignment. That also means that if you remove the metal on the wrong side, you only slowly increase the error.
You need to keep the test bar in the head stock/chuck for checking the alignment. That makes the head stock quite heavy.
I used a self made test bar because this test bar has no runout and that makes checking the alignment easier.

Once the headstock is aligned, you can align the tail stock.
Some lathes have a headstock that allows changing the left/right angle by rotating the head stock around a swivel point.

If you bolt your lathe to a rigid stand, you can twist the lathe bed causing mis alignment. So my mini lathe and bigger lathe are not bolted to the stand.
The rigidity of my bigger lathe would surely benefit from bolting to the stand but the concrete floor would influence the lathe alignment when the temperature changes (summer/winter) and that is a no-go for me. My shop is on the first floor (pre tensioned concrete plates)!

The paint should not dry so quickly. You can use an "art painters oil based paint" that is available in small quantities. Any dark (Blue, Red, BLack) colour will do.

I have "scraped" the saddle of both my lathes. For scraping I used a diamond dremel disk (not the dremel) and sanded the high spots on the saddle (not the bed) only the flat side, not the V shaped side!
I measured the tilt on the saddle edges using an indicator and stopped sanding when the indicator did not move when I pressed on the edges of the bed. I used the sharpy method to find the high spots.
After sanding with the Dremel diamond disk, I sanded the sides using a 1000 grid paper.
It is a time consuming but "easy" job and it will improve the rigidity and accuracy of the lathe. It is also the first thing to do before aligning these parts.

I did the same with the head stock and tail stock of both my lathes.

I also can't bolt my mini lathe (HBM DC300) down to the table so I can't align the head stock by shimming. I have taken the head stock of the bed and scraped/sanded the seating of the head stock so that it aligns OK (0.015 mm/100 mm). It took me a day to do it. That is however not easy to do because to remove the head stock, the electronics, gears and motor have to be removed first.