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Member postings for Mike Donnerstag

Here is a list of all the postings Mike Donnerstag has made in our forums. Click on a thread name to jump to the thread.

Thread: Myford Super 7 Spindle Runout
21/06/2022 15:30:43

Many thanks to everyone who replied.

Tony: It is radial run-out, which I measured on a ground spindle held in an ER40 collet chuck, with a backplate screwed onto the spindle.

Martin/blowlamp: Measured on the OD of the the spindle register, the total runout I can measure with my half-thou indicator is around 0.0007" when in lowest back-gear. Perhaps this isn't too bad - let me know what you think. I hadn't realised that the oil film in the front bearing needs to stabilise. How does this affect DTI readings?

The belts have been recently replaced and I have also adjusted the bearings recently.

My theory is that the balls in a ball race rotate at half of the speed of the spindle. Am I right?


20/06/2022 18:50:58

I have a Myford Super 7 and have found a half thou runout that only occurs every two revolutions. Am I right to assume this is the rear bearing that is at fault?



Edited By Mike Donnerstag on 20/06/2022 18:51:26

Thread: Turning between centres on Super 7
20/02/2022 14:51:56

I just found this old thread on Myford centres, so I thought I'd reply.

When I bought my Myford it came with many accessories. Among these were three centres that are shorter than standard: soft, hard and half centres. I expect these were originally supplied by Myford to be used with the relatively short pin on the standard catch plate and their bronze drive dogs. Coincidentally, I made a longer pin for the catch plate recently, to work with a standard centre (forgetting I had the shorter centres!).

I notice from the Myford literature that as well as supplying the standard hard, soft and half centres for metal turning, and the hollow and wood prong centres used for woodturning or with a drill pad, they also supplied square centres and fluted centres. Does anyone know what these were used for? I can't even picture a 'fluted centre'. The square centre had a steep square taper on the front; in fact there is one on eBay at the moment.


Many thanks,


Edited By Mike Donnerstag on 20/02/2022 14:52:19

Thread: Head or quill feed when slotting
07/01/2022 19:18:02

Very interesting. Is a 3-flute cutter therefore a good all-rounder, or do you still use 2 and 4-flute cutters for specific purposes? Please excuse my beginner questions and feel free to point me to a thread if one already exists on the topic.


Thread: Sieg SX3 Z axis adjustment
07/01/2022 19:01:49

Andy: I am having the 'clunking' problem with my SX3. Would you say this is due to the gib too tight or too loose?


Thread: Sieg SX3 and Machine-DRO 3-Axis Kit
07/01/2022 18:55:41

I am still having issues with my Sieg SX3 Z-axis in spite of experimenting with the adjustment of the tapered gib. When moving the head with the handwheel, there is a mechanical judder that is shown on the following YouTube video:

The judder is worse when lowering the head, and only occurs when moving the handwheel slowly. As shown on the DRO, each 'judder' is about 0.05mm in travel.

Is this normal?


Edited By Mike Donnerstag on 07/01/2022 18:56:53

Thread: Head or quill feed when slotting
07/01/2022 18:35:39

John: Apologies - I didn't explain myself well. According to the 'Warco head shake' post, Old Mart posted the following:

"I remember plunging a 1/4" slot drill about 1/4" deep and getting a hole 0.015" oversize. Changing the cutter resulted in a hole only 0.001" oversize, yet there didn't seem to be much difference in the sharpness."

From this, I assumed that it must be the cutter geometry that is different between the two 2-flute cutters. I watched JasonB's Youtube video that showed a trouble-free plunge using the z-axis, again surmising that it was the quality of my cutters that may be at fault.

Also, I should have changed the word 'lower' to 'move' as this obviously only applies to the Z-axis and not the X-axis.

By 'fully enclosed' I mean that the slot starts and ends within the metal. The cut was blind (not through) and about 5mm deep overall. I took this to depth in 0.5mm passes.

In a previous post, JasonB explains that ArcEuro recommend using the quill feed for plunging, rather than the Z-axis. Having tried both, at least using the poor quality bit I have, it was evident that the quill feed was more controllable.

JasonB: Many thanks for your advice. That's exactly what I should have done. Can you also mill the slot using the 3-flute cutter, or would you switch to the 2-flute?

07/01/2022 17:31:31

Apologies for the very late reply! I read all of the comments (many thanks to all) and realised I had neglected to say that the slot I was milling was fully enclosed, necessitating plunging. It was the plunge that gave me trouble, resulting in the head shaking (both the milling machine's head and mine!)

I stripped and reassembled the head and column using the ArcEuro Sieg SX3 dismantling and reassembly guide, ensuring everything was lubricated, adjusted and working as it should... though to no avail.

Since then, I since found a similar post:, describing the same problem but with a Warco mill of a similar size. I conclude the following from the thread:

  • The HSS 2-flute bit (from a cheap set) I was using was probably asymmetrically ground, resulting in the violent vibration/shaking
  • Plunging using the Z-axis with the quill locked may have worked if I had used a better 2-flute bit. Alternatively I could have plunged with a 3 or 4-flute bit or drill bit and switched to a 2-flute milling bit for slotting
  • Ramp cutting (lowering Z-axis and X-axis at the same time) would have worked better
  • Locking the head and feeding using the quill would have been better (as ArcEuro recommend) - this was the method I used in the end

Let me know if anyone has any comments on this. I realise that a sturdier, commercial mill would be more forgiving!

Many thanks and Happy 2022 to everyone.


Thread: Macc Models Excellent service
23/12/2021 17:08:20

I can also recommend them - great service.


Thread: Head or quill feed when slotting
08/12/2021 17:26:05

I have a Sieg SX3. I need to run a slot along the side of some mild steel (a finger clamp) to allow it to be bolted to the mill table.

I am using a 6mm 2-flute slot drill and I'm not too bothered about the finish or the exact size, so I'm using this to mill a 6mm slot.

My question is, should I lock the quill and use the head feed (Z-feed) and the three axis DRO that I fitted, or should I lock the head and use the quill feed? Which is best?

I tried the former (locking the quill and using the Z-feed) and the mill started to shake. Is this due to movement on the pillar dovetail? I had more success with the quill feed, milling the slot in about 0.5mm increments.

Many thanks in advance,


Thread: Warco HV6 rotary table
04/12/2021 21:22:27

Apologies for hijacking the thread, though it is relevant. Especially when it's the Warco 10% off weekend!

I have a Sieg SX3 mill and wondered:

1) Is a 6" rotary table recommended or would you recommend a 4"

2) How does the Warco HV6 (Vertex style?) rotary table compare to the equivalent ArcEuro one, which is significantly more expensive? JasonB - I understand you use the ArcEuro one

3) Would the hole spacings allow the HV6 to be mounted vertically on the SX3? (Does anyone have the minimum and maximum hole centres for vertical mounting?)

Many thanks,


Edited By Mike Donnerstag on 04/12/2021 21:32:49

Thread: Help with Electrics on a Bow Bending Iron
19/05/2021 18:19:28

Many thanks for all of the information. All of your comments will be taken into account.

The iron is not a commercial product. There are frankly too few bowmakers to make such a product worthwhile developing. The metal covers conceal thermostats, limiting the temperature.

I will check to ensure the iron is functional and make some changes to improve its safety based on all of your comments.

Once again, many thanks to all,


16/05/2021 16:57:40

I recently acquired a large iron for pre-bending musical instrument bows. The tool consists of two large aluminium blocks in which several heating elements are inserted. These are wired (using their own heat resistant wires) to ceramic connectors/terminal blocks which in turn are connected to a thick flex and a 13A plug.

While the metal parts on the tool are well earthed, the fact that much of the electrics is exposed worries me, particularly the exposed screws on the terminal blocks.

I wondered whether there are any electricians amongst you who could advise on the best way to make the electrics safer and less exposed. Obviously any solution would need to be heat-resistant.


Thanks in anticipation,


Thread: Sieg SX3 and Machine-DRO 3-Axis Kit
13/05/2021 12:15:12

Apologies for the delayed reply.

In response to James' questions:

The magnetic strips are easily cut to length. I think I just used tin snips. The aluminium extrusions obviously need to be cut with a hacksaw.

The mounting for the display is fixed to a thick aluminium plate behind the pressed-steel cover. This reinforces the mounting substantially.

Regarding my thinking behind how I mounted the scales and readers, it was all about future-proofing. Specifically, my objectives were:

1) To leave each of the three scales as long as possible to potentially mount them to a different machine in the future

2) To ensure the ends of the table are completely clear of mounting brackets, etc., to allow a power feed or even CNC motors to be mounted in the future.

I think this answers your questions so far.

I am still not too happy with my Z-axis readings. I think this is due to the 'spring' in the machine between the movement of the leadscrew nut and the head movement. I haven't investigated whether this is the gib adjustment, which may be a little tight, or whether it is fundamentally the fact that the reader is some way from the head. The travel of the feedscrew nut, to which the reader is fixed, doesn't perfectly follow the height (Z-position) of the head. The movement also seems to be too juddery to rely on for accurate height settings, hence why I use the quill for accurate height settings.

Jason: I'd be very interested in your thoughts on this. Specifically, would you expect to be able to set the head height just as accurately as the quill? Also, do you have any hints on how best to set the head gib so that it's not too tight or too loose? (Perhaps this is one for Ketan?)



Thread: Tapping Mode on Mill
15/04/2021 19:05:21

Thanks Andrew and JasonB. It's a bracket for securing a small toggle clamp (Brauer P50). I don't think the thread needs to be that deep, though I'm happy to over-engineer it. I'm obviously on the limit of what a machine tap is capable of, though I expect a larger tapping drill would definitely help. However, for this application I think I'll revert to hand-tapping, guided (at least at the beginning) by a tap follower. I dare not risk another scrapped bracket due to a broken tap.

Once again, many thanks,


15/04/2021 18:31:52

I hope nobody minds me asking a related question. I tried tapping an M4 through hole into 15mm thick mild steel using my Sieg SX3 mill in tapping mode (at about 150rpm), using an Arc-Euro spiral flute tap. The tap made it through two of the holes, with a bit of a struggle, but broke in the third. The holes were all drilled with the usual 3.3mm tapping drill. The tap was held in an ER20 collet chuck, which in turn was held by its 20mm shank in an ER32 collet chuck, held in the machine taper. I used plenty of Rocol RTD cutting fluid.

What did I do wrong, if anything? I understand that a spiral point tap would have been more suitable for a through hole, and perhaps may have been less likely to break. I realise 15mm is quite deep for an M4 hole; could that have been the problem?

Any help gratefully received, as usual

Cheers, Mike


Edited By Mike Donnerstag on 15/04/2021 18:33:34

Thread: What is this? Something to do with hardness?
23/02/2021 16:56:45

Thanks Michael.

Perhaps a better question would have been: Is it worth anything to anyone or should I scrap it?


23/02/2021 16:48:50

I acquired this metal block many years ago. It appears to be etched and comes with its own wooden box. Can anyone tell me what it is used for?

Many thanks,


s-l1600 (1).jpg

Thread: Truing a hardened half centre on a Super 7
05/11/2020 22:30:26

Thanks to all who posted. Though I wouldn't do it again, I've learnt a bit more about using carbide on hardened steel, and what is possible on a Myford.

For interest, what do you chaps think about hardened vs. carbide-tipped centres?


04/11/2020 14:09:09

Perhaps I'm nuts even attempting this. I have a half-centre that had been badly ground from a normal (full) centre by a previous owner . The centre wasn't true, nor was it at 60deg to match a centre drill.

I tried using a tool with a CCMT insert to attempt to true the centre. I quickly realised that that the centre was hardened (that's probably when I should have given up!) Anyway, I persevered... I increased the rigidity by locking the carriage and cross-slide and tightening up the gib screws on the top-slide a little. I ran the lathe at 420rpm and set a depth of cut of around 10thou, using Rocol RTD to cool and lubricate the cut.

I ran the top slide slowly from the large to the small diameter at first, though the interrupted cut soon broke the tip off the insert. I tried another insert, this time a Kennedy, as the first insert came 'free' with a cheap eBay insert holder. Again the tip soon broke with the interrupted cut.

Not wanting to be beaten I then tried a third corner (turning the Kennedy insert 180deg), this time running from the 'solid' small diameter to the larger diameter. It cut well until it got halfway up the edge, and once again the interrupted cut broke the tip. However, the centre is now usable.

I assume the ideal way would have been to use a toolpost grinder, or perhaps I could have annealed the centre and re-hardened once turned, though that would probably lead to distortion?

Looking at the cost of centres, I obviously spent more in carbide tips than the cost of a new ground centre. My question is, had I attempted the impossible, or is there anything I did wrong or could have improved? I'd really be very interested what people think.

Many thanks,

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