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Member postings for Marcus Bowman

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

Thread: Machining - sitting or standing?
08/09/2014 17:15:50

I endorse the "standing" comments. I stand at the lathe, drill and mill, but have a bar stool handy to relieve the pressure on the knees and feet occasionally, if required. I also have relatively high benches and use the same arrangement, with a modified telegraphist's chair (high central pole, and a ring near the bottom for feet to rest upon). The chair has been extensively modified so that it has a comfy cushioned seat and back, so that sitting is a pleasure. In fact I now have two of those chairs (second one came from a local building site) so I can entertain a friend in the workshop in relative comfort. That takes the pressure off the feet too.

The only problem with having stools or seats in the workshop is that they rapidly become handy places to put things down "just for a minute"...


Thread: A variable Lead threading attachment. Author Ted McDuffie
13/08/2014 19:24:55


I have sent you a PM.


Thread: How to centre a boring bar
13/08/2014 14:30:54

I sometimes use a Laser Centre Finder in the tailstock chuck. It shines its beam right along the lathe axis, so you want to adjust the cutting edge to split the beam, so to speak. I use a Polarising filter to get a really small beam.


Thread: DRO using a wire
07/08/2014 22:47:07

I have two of these units, and would not be without them. They are in daily use. One of the advantages is that the wire can be routed vai pulleys so that the unit itself can be conveniently located while the wire is routed to a slightly different pickup point not directly aligned with the point at which the wire exits from the unit. On my drill, I have the unit clipped horizontally at the front of the head of the drill, and the wire is run around two pulleys to drop vertically down the right hand side of the spindle, to a projecting pin.

On the lathe, I have one permanently clipped to the bed so that it measures carriage displacement.

The units mount via large clips, so I can take the drilling machine unit and clip it onto the tailstock, measuring barrel travel.

I have a clip to allow a unit to be clipped on the carriage to measure cross-slide travel, but don't use it for that, as the resolution is not high enough. That's an issue often overlooked with the cheaper digital scales, so its not unique to this BW unit.

The features of the units are quite extensive, and they have 9 selectable travel measurement displays, so that for a mass production job I can turn to a shoulder, select the next position and turn another feature, etc.

The units I have are single axis free-standing units and they do not link to a central display.

Expensive - yes. Worthwhile - I wouldn't be without mine; to the extent that I have been considering buying a third unit (saving up, at the moment; and thinking about my Christmas List).


Thread: Avoiding marks on work.?
26/07/2014 09:33:14

I use brass or aluminium shims, but bent so they loosely grip the jaws to prevent them falling out as I try to juggle 1 workpiece and 4 shims and a chuck key with only 2 hands. I find it also helps to seat the work against two adjacent jaws before tightening the other two, so that the jaws sit square to the work and avoid constant sideways thrust.

In a 4 jaw, lots of damage occurs because as the jaws are finally tightened the work is sometimes moved sideways to finally line up on a mark, and the gripping jaws wipe across the work surface. Shims help prevent that.

Gripping against the reversed jaws sometimes helps too, although the corners of those curved faces can be fairly sharp too.

It's also a good idea to leave a little extra material on the work, to be removed or finished later, if possible.


Thread: Making A bolt for my motocycle
26/07/2014 08:56:09

I have used EN24T recently for some stressed parts on bikes and on machines. It machines very nicely using carbide tools or HSS tools. I have cut threads, rather than use a die, mostly because of the nature of the thread I required, but a HSS die will work. The steel would need further heat treatment afterwards, to give it the hardness/strength characteristics to match a high tensile bolt, and while the machining is easy, getting the heat treatment done is a pain.

Stainless is not an appropriate material for a highly stressed job, as it is "softer" and less strong than most of the EN16/24/57 steels. Stainless sets up corrosion against steel and aluminium. I see lots of fasteners in stainless, now, including many small diameter fasteners, but I don't believe it's a good choice for every situation, especially small (M2) fasteners with an internal hex (like a grub screw). Some grades of stainless are not corrosion-proof.


Thread: Soba Vice Problem
26/07/2014 08:46:32

Yes; Chris is right:

You generally get what you pay for.

and that's especially true with tools. The same has happened with tools as with many other consumer products; the price has determined the quality. The more low cost tools we buy, the less top quality tools are available to buy, so we've pretty much shot ourselves in both feet by pursuing low cost at any price(!)

There is an awful lot of stuff out there that looks nice (and cheap) but is made of cheese and badly put together. Ultimately, we pay for the tools in the time and effort we have to expend in making a silk purse out of a sow's ear. That's difficult for someone starting out with a workshop, because it often takes expertise to be able to end up with something that works, is accurate, and does the job it would have done in the first place if we had paid top dollar.

For some folk, trading time for a saving in money is fine; but for others it's not such a good deal. It depends on what you want to spend your time doing, of course.


24/07/2014 23:00:20

What is also useful is to make one hole a good fit for a bolt with a short unthreaded portion under the head (a "fitted" bolt). Elongate the other hole in a north-south direction (i.e. elongate towards the front of the mill or drill bed and towards the back. The fitted bolt makes it easy to swivel the vice a little, and the elongated hole ensures you can bring the jaws parallel to the direction of travel of the mill table.

A better way is to make a vice plate (see MEW 206, page 18; MEW 207 pages 16 to 19; and MEW 208 pages 18 to 20 - and note that the plate can easily be made by non-cnc methods). It won't matter whether your vice holes are aligned or not. Simply set up the plate with a reference edge across the table, set the vice on the plate and clock it true, then mark the positions you need for the vice bolts.


Thread: Hammerite has changed
16/07/2014 19:06:58

I have used the new Hammerite, and its the last time I will buy it. The new version is a completely different formulation, like almost all paints currently produced, and its composition has been changed to conform to current regulations. A paint supplier will confirm this.

The old Hammerite was based on glass flakes and was marvellous stuff (1970s) but subsequently changed in, perhaps, the 1990s to its detriment. Still worked to some extent (but I can tell you the weather resistance was much reduced). Changed again, totally, a couple of years ago.

I have now used up my old stock, and have had enough of the new stuff. It's a huge disappointment.


Thread: Bending thin walled brass tube
16/07/2014 19:01:05

Yes; Cerrobend (now called CS Alloys Bend 158) will do the trick. I use it for bending thicker walled steel pipe, but it is easy to use and will avoid all kinking and distortion of the tube. You may still want to use a spring or a bender with formers, but the Cerrobend will still prevent damage. I use it in steel to allow bends with much tighter radii than can be achieved using a conventional former-style bender. In fact, I use the kind of bender that is normally used for flat bar or solid circular bar, and can get tight bends.

You can get small quantities on eBay. It is relatively expensive, but is designed to be re-used.

Melt it in boiling water, a bit at a time, then pour it into the tube. Let it set (doesn't take long); bend the tube, then heat the tube and the Cerrobend runs out. I run it into a tray normally used in the oven for making cupcakes, so I end up with little thick pancakes of the material, which go back into the drawer afterwards, ready for next time. You don't want a big solid lump because although it melts at a low temperature, it takes ages to metl a lump in boiling water. I dare say you could melt it with a hotter source, but the fumes are injurious, so a layer of boiling water helps keep the fumes at bay. face mask, goggles, and outdoor working are my recommendation.

Jolly handy stuff.


Thread: How do you solder brass cones/nipples onto copper pipe
13/07/2014 17:36:46

Yes; Loctite technical staff are very helpful. I do know that Loctite works best when the parts are pushed together under a light interference fit, so it may be possible to machine the nipples for that condition to apply. The idea is to exclude air, and it seems this works best when the film of adhesive is sheared as the parts go together, leaving the bond to be made by very thin layers of adhesive which are left in the microscopic interstitial spaces between the components. I always thought I should leave a little clearance for the adhesive, but, having taken advice about replacing a press fit between two components by using Loctite, the advice I as given was t go for a light press assembly, having first coated the mating surfaces with Loctite. Worked extremely well, and the components are still together, despite heavy loading of the joint.

In the case of a nipple, I would guess that a light finger-push fit is what would be required.

It might also be a good idea (and a slight complication) to ensure the tube was round and of the correct diameter, perhaps by inserting a rod, and squeezing the outside of the tube very lightly between two halves of a hole. Clamping two rectangular blocks together, and drilling a hole down through the joint would give an accurate former.

I think all of this is, as you say, a very interesting experiment. It also highlights how developments in adhesives challenge our preconceptions.


Thread: Reaming mild steel.
11/07/2014 08:50:37

Speed and pilot hole are about right, although I use 15.8 pilot (depends what you have to hand, really) i.e. 0.1mm undersized up to 8mm, 0.2mm undersized above that. Lots of neat cutting oil lubricant. I can't say if the use of soluble oil will affect it, but I believe the neat oil is a better lubricant (rather than a coolant). Peck ream, removing chips frequently as the reamer descends quite slowly, in stages, withdrawing at each stage and brushing the chips off then lubricating. You should get a decent smooth finish. I did a 12mm hole yesterday and it looked good to me. What grade of 'mild' steel? EN1A or EN1A with added lead should both give good finishes (the leaded version being better). Maybe the odd scratch visible. EN3B (which is what I used yesterday) should also give a pretty decent finish but with a few more scratches visible.

What are the edges of the reamer teeth like, viewed under a loupe or a microscope?


Thread: How do you solder brass cones/nipples onto copper pipe
11/07/2014 08:39:25

That's a good idea, Julian. The bits that are most prone to overheating seem to be the sharp ridges or the corners, and the very fine end where the tapering cone meets the pipe, so the mating adaptor would cover those. I can also recommend putting the assembly inside a larger steel tube and heating that, so the pipe and nipple receive only indirect heat.


11/07/2014 08:18:00

Just returning to the heating issue for a moment:

there's a balance to be struck here, I think. My experience has been that small torches (e.g. the Proxxon small 'cook-sized' torch) are very handy for tiny jobs, but will not do for larger jobs or for jobs where more heat is required such as copper pipe. I have a larger propane torch (Sievert, I think; but very old) which has a fine jet or a broad jet. That's a better bet, and can also be used along with the Proxxon. Of course then you need 3 hands... I use that combination for hardening and tempering small jobs.

Then there's the oxy-acetylene... which inevitably just melts small jobs. Wonderful tool, but not for nipples.

I thin it best to have adequate heat, and some in hand, because one factor is the ability to bring the work to temperature quickly. If it takes too long the flux will boil off. Once the flux has gone there's little chance of actually achieving a decent job.

Loctite is wonderful stuff and I use it often, but have not used the high temperature stuff.

Grade 4090 says it is ok to 150 degrees C, but I have not used that product. Others are ok to 100 deg C.


09/07/2014 23:12:29

Cleanliness is an essential factor for success. As is a good fit: not tight, but just a suspicion of looseness - but not a rattling fit either. There should be just enough clearance to allow the solder to be drawn into the job by capillary action, but no more.

Flux the joint well, then (as mick H suggests) avoid heating the nipple directly. As you have discovered, the danger with direct heat is that the nipple melts. Apply enough heat to bring the job to temperature quickly.

I agree that solder paste is a good idea. A ring of fine silver solder wire around the top of the joint is a good idea instead. As noted, quality of solder is important.

Thread: Another homebrew CNC miller
16/06/2014 23:24:03

Ballscrews alone, especially small diameter ballscrews, don't have zero backlash. You would need two nuts per screw, adjusted to eliminate the backlash. What ballscrews do offer is a relatively constant backlash along the length of the screw. Ground screws have less backlash than rolled screws.

Yes; you are right: good mechanics don't come cheap, but they are essential if you are to realise the promise of CNC. As usual, you won't get what you don't pay for...

I am also of the opinion that just because the workpieces will be small that doesn't necessarily mean the CNC machine will be small. Modern Swiss watchmaking machines tend to be large and heavy, if pictures are anything to go by. Size and weight are associated with rigidity, and that's often a problem when making DIY CNC machines. In fact it is a problem with many of the commercially available small mills etc (Hobbyhorse...).

One way to be able to use large diameter screws is to use differential screws which effectively provide a fine pitch despite the screws themselves having a coarser pitch. Expensive, though.

A problem with a fine X or Y feed is that when machining small parts you will need a high spindle speed and fast feeds to allow the cutter to cut efficiently.


Thread: Advice required regarding escapements
16/06/2014 23:06:17

You might like to know (if you don't already have the information) that the East of Scotland branch of the British Horological Institute meets once a month in central Edinburgh (in a room in The Canon's Gate, 232 Canongate). There is always a good attendance, and lots of advice is freely available. They are a friendly lot. Next meeting is not until September, because of the summer holidays, but if you would like further details, just let me know, as I attend the meetings.

That would be an easy way to have a face-to-face discussion.


Thread: Machine plate grouting (most common method)
01/05/2014 22:48:06

There is a large, long-running thread about epoxy/concrete fills here:


Thread: CNC in the Workshop - Part 9 Typo
29/12/2013 08:08:03


My apologies, but there's a typographical error in Part 9. It's my mistake, and no-one else's. Rushing to meet a deadline, and thinking of two instalments at once, confused both of my brain cells.

On page 9 of issue 211, dated January 2014, in the left hand column, a few lines above fig 44, the line beginning:
“We can specify which mode we want”
should read:

“We can specify which mode we want by using the command G91.1 to set Incremental IJ mode, or by using G90.1 to set Absolute IJ mode.”

Note that the G92.1 printed in MEW is incorrect. We will meet G92 and G92.1 shortly, but those commands do something quite different to G90.1.

I realised my mistake before publication, but too late to have the copy corrected before printing, so the error has been flagged on the support website at from that point.

I thought it useful to repeat the note here, for anyone reading the articles but not visiting the support website.

Although annoying, the error should not cause any great practical difficulty at this stage, because the incorrect command is not used for anything in a practical program in that instalment and the examples use the (correct) G91.1 command.

While we are at it, and just in case you haven't already seen it, you should note the missing minus signs for the Z values, in Part 6. Those have been flagged for some time, in the helpful post on this Forum by John Haine (Error in CNC Article) and on the support website. Thanks, John.



Thread: Thread Milling
29/08/2013 23:28:51

As far as I understand, if you are moving "normally" in X, Y and/or Z the same feed rate applies to the movement of the CP within that co-ordinate space. I think that means that if you are moving anywhere in X, Y or Z (including at an angle in two or three of those axes simultaneously) movement occurs at the feedrate set by the F command.

There is only one F command, so it is applied to X and/or Y and/or Z and any combination of those.

If you are using one of the other feed rate modes like inverse time mode, I believe different rules apply.

The more interesting question is how well does the control software cope with acceleration and decelleration while thread cutting? A first guess would be that it copes fine. A caveat is that some CNC-cut threads seem stiffer in the mating thread than they should be, and although this might be because the depth of cut is not adequate, the feel of the thread suggests the depth is fine and it is a problem with the approximations.


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