Member postings for Y C Lui

Gray, Thanks for taking time to do the test. You are probably right because I am not seeing any problems in actual use of the machine. The finish of face milling is good and I am getting good accuracy ( within 0.01 mm ) in the dimension of the workpiece in the Z axis ( not so good for X & Y though ) so I think I will leave it as it is.

The instrument is called "Z axis tool setter" which is used for setting the height of the tool tip above the mill table precisely so that you can have a reference point to locate the tool relative to the surface of the work piece along the Z axis. It's just a locating tool like edge finders but it works on the Z axis.

The shift of the spindle position along the Z axis is as much as 0.05 mm. Having this magnitude of free movement should guarantee bad finish in face milling but I am not seeing that. As of now I tend to believe that the shift is there by design although I can't figure out what the purpose is and how the bearing is constructed to achieve this.

Edited By Y C Lui on 07/02/2022 14:26:46

What you suspect is very reasonable. I used the Z-axis tool setter in the video just because the dial is facing the camera at all time so the correlation between the needle movement and the rotation of the spindle can be seen clearly. Just to eliminate the possibility of inclined tool setter top + collet run out being the cause I have checked again with a totally different set up as shown in this new video.

The table of the mill is not perfectly level though. On the Y axis, the TIR seen in sweeping the DTI over a distance of 150 mm is 0.04mm ( are there any ways to eliminate it BTW ? ), On the X axis, the tram is close to perfect after adjusting the tilting of the head.

Edited By Y C Lui on 07/02/2022 14:01:14

I cannot imagine DRO being off-cal by as much as that. Comparing the DRO reading with the hand wheel scale reading should give you some good idea on what's happening.

Edited By Y C Lui on 07/02/2022 02:53:01

Thanks for sharing. This is a very clever method, no cutting needed. The rod just need be reasonably true round at the ends, it can be bent or tapered. Just tried it on my lathe and happy to see that the alignment is close to perfect

Edited By Y C Lui on 07/02/2022 02:21:57

If this is my lathe ( an Emco Compact 8 ), I will definitely say it's due to flexing. Having said that, your lathe is much beefier so there may be other reasons. To minimize flexing, I need to reduce the cutting load to absolute minimum so the rod I have made for such purpose is composed of two ABS plastic discs glued to the ends of a steel rod. In this arrangement, the cutting load is almost zero. You may try using aluminium in your case and make sure that the tool is super sharp. ie, either HSS or grounded carbide tool ( instead of molded )

Edited By Y C Lui on 07/02/2022 02:05:21

Not sure how it can be done ..... anyway, this is the construction of the spindle / quill of hte machine :

**LINK**

Here is the video with the tool changed to one with a ball end. The result is the same.

The video

I don't think the measurement system has anything to do with it because this was first noticed with an entirely different set up in which a DTI was connected to the spindle for checking the tram of the machine. It was the inconsistent tram measurement that led me to discover the issue.

Edited By Y C Lui on 06/02/2022 11:33:03

I was checking the tram of my Emco FB2 mill today and found something really puzzling. The mill seems to be unable to hold the Z axis position depsite the fact that both the quill and the Z axis were locked. At first I thought the DTI holder of the DTI itself has got something loose but after further checking, the problem seems to come from the quill. The Z position change is as much as 0.05 mm or 2 thou but the wierd thing is the shift depends on the direction of rotation of the spindle prior to taking measurement. I have tried to move the chuck vertically to see if there is any play but there is none. The small deflection of the DTI is just due to the relatively weak rigidity of the machine.

Video showing the issue

No related issues was seen in actual use of the machine. The error in the Z-axis direction is within 0.02 mm.

Any thoughts ?

Edited By Y C Lui on 06/02/2022 06:58:25

For me, it's the opposite as I use the DRO all the time. Reading the handwheel markings is OK but the resolution is 0.025 mm instead of 0.01 / 0.005 mm for DRO. With the handwheel, you have to count the number of turns and memorize where to stop but with DRO, you just move the tool until the reading is zero. It's far more convenient and less error prone. This is for the Y-axis.

For the X-axis, I have tried to avoid it by repeatitively measuring the distance and calculating the incremental movement of the compound side needed but finally got frustrated and switch to DRO. Happy ever after. For me it's the most-used accessory for my lathe.

Edited By Y C Lui on 16/01/2022 09:47:08

Shims ? I don't have any because I use carbide inserts only. The bottom of each tool bar is milled to make the tip of the insert line up with the center of rotation of the spindle. If the tool bar is too thin, a steel plate will need be epoxied to the bottom before machining. Once done, there is no need for any re-centering in future use. Just mount the tool and start cutting. Here are some of my tool bars ( bottoms facing up ) :

Edited By Y C Lui on 15/01/2022 18:40:41

I have bought or made a number of accessories / tools for my Emco compact 8 and I found the followings to be the most useful :

1) DRO. I made one from digital caliper for the radial direction. It's permanantely fixed to the carriage. It helps A LOT to improve the precision. With care, the error in the final diameter the workpiece is not measurable with a 0.01 mm resolution caliper. Recently I made a holder for mounting a digital caliper to measure the X-axis movement.Will likely switch to a optical scale later.

2) Carbide tools. They are cheap today and come in a wide variety of geometries and types. Molded, grounded, for steel, for aluminium .... so I don't bother to grind and center HSS tools anymore.

3) Carriage stop. An essential safety device when you need to get the tool very close to the jaws of the chuck.

4) Tap and die holders going onto the tail stock.

QCTP ? Quite appealing to me at the beginning but after thinking it over, I finally decided that they are not needed for my use.

Edited By Y C Lui on 14/01/2022 14:53:27

cutting aluminium stock of that diameter at 435 rpm is certainly no issue but for mild steel, I have some doubt. It will not work on my Emco Compact 8.  Most info on line says that the RPM need be halved or the tool will just be rubbing instead of cutting. That's assuming that the torque of the lathe is good enough to maintain a steady speed under the cutting load. Otherwise, the cutting speed will need be lowered further.

I am not sure if you have a compound slide so that the tool can travel parallel to the surface of the chamfer instead of along the axis of the disc. Without that ability the cutting load will be increasing heavy as the width of the chamfer increases. At some point, the motor stall.

May be you really need to explore the option of slowing down the lathe and increasing the torque as previously advised.

Edited By Y C Lui on 12/01/2022 14:51:11

This is a way to reduce the speed to 178 RPM and increase the torque at the same time  : https://www.micro-machine-shop.com/taig_motor_mount.htm

Edited By Y C Lui on 12/01/2022 06:59:43

The OP mentioned that the prime purpose is to turn a steel disc that was too big to be held by the original chuck. If the steel disc is too large, say, more than one inch in dia, then the lathe will need be slowed down ( or more importantly, has the torque increased ) in order to do the job.

There is no info about the shape of the disc or the kind of cut that need be made but holding this kind of workpiece by clamping the outside is not workable if the cutting is to reduce the outside diameter. Even if it is workable, soft jaw will be an expensive solution at least for me if it is just used for making one piece of parts.

For me, I will seriously consider using glue, either super glue or epoxy.

Edited By Y C Lui on 12/01/2022 04:08:47

I haven't tried the super glue method but I think that should work quite well in the OP's case because the workpiece has a relatively large surface area.

For the OP's reference there are Youtube videos showing the method used by professionals and amateurs on big and small machines : 

https://www.youtube.com/watch?v=r6DCvtcU8_M&t=110s

https://www.youtube.com/watch?v=0svTlISjr3s

Edited By Y C Lui on 10/01/2022 16:17:26

I didn't express it clearly but I meant the OP will need to replace the existing motor with a DC brushless type to realize his "plug and play" solution of varying the speed steplessly by simply turning a dial.

Edited By Y C Lui on 10/01/2022 16:08:32

The range of speed should be good for turning aluminium.on my bench lathe (Emco compact 8) I use 1700 rpm for most of the time. I reduce speed only if the diameter of the stock is on the large side. What is the problem you are having? The set up mentioned in your post uses DC brushless motor. You will need to replace the existing motor which is not a trivial task

Thanks for all the replies. Really appreciate it. Gray's reply suggests that this can be a common problem of FB2s. Glad that the problem can be solved / alleviated by changing cutters. I will explore further in that direction. May be trying out 3 fluters designed for cutting alumnium ( no coating , rake angle may be larger as well )

I have subsequently done further checking as suggested by Joe and Kiwi Bloke. The set up is shown in this photo

With all the axes locked except for the Y axis. I pushed the table at the right and left sides with all the muscles I have got and the indicator reading only changed by about 0.003 mm.

However, when I pushed the mill head with relatively little force. the change in dial reading was 0.015mm, a lot larger. Checked all the six screws mouting the column to the base, all are super tight. Then I followed Joe's suggestion to loosen the two set screws on the column slide. Doing so is to take out any excessive play between the slide and the column. This was confirmed by the fact that I could not move the slide even if the Z-axis locking level was loosen. With this done and the Z axis locked up again, the sideway movement of the head upon being pushed was just reduced very slightly to about 0.012 mm. Then I did a test cut and the finish was just the same, ie, still bad.

Can it be concluded that the bad finish when cutting along the Y axis is due to the poor rigidity of the head along the X axis ?

Edited By Y C Lui on 09/01/2022 12:49:15

Hi Joe,

Thanks for the reply. I have created an album and the photos can be viewed here :

Typical finish of side milling along the Y axis :

**LINK**

Test cut set up ( milling along the X axis ):

https://www.model-engineer.co.uk/sites/7/images/member_albums/111244/902861.jpg

Difference in finish. X axis vs Y axis : 

https://www.model-engineer.co.uk/sites/7/images/member_albums/111244/902862.jpg

The sound is the same when cutting along the X axis ( good finsh ) and Y axis ( bad finish ). There is not any chattering sound although the finsh may indicate some chattering is happening when cutting along the Y axis.

Yes, I have tried increasing the feed speed from about 80 mm/min to 200 ( manually done so it's just a rough indication ) and the result is just the same. Comparison :

https://www.model-engineer.co.uk/sites/7/images/member_albums/111244/902866.jpg

The quill taper is in very good condition I would say. I have got a Big-Kaiser boring head with a tang-end taper and it never dropped out by itself. I bought the mill new some 25 years ago and never used it much until now. This is just a hobby-grade machine so I do not expect a lot from it. What puzzles me is why the finish of side milling is so different for the X and Y axes. I have asked about this in the hobby machinist forum. The guys there have no clues and referred me to this forum for assistance.

Edited By Y C Lui on 09/01/2022 07:32:27

Edited By Y C Lui on 09/01/2022 07:33:25

Edited By Y C Lui on 09/01/2022 07:36:29

Edited By Y C Lui on 09/01/2022 07:42:58