cutting BMS, filing edges of cut BMS

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cutting BMS, filing edges of cut BMS

This topic has 17 replies, 13 voices, and was last updated 4 May 2011 at 13:27 by Lawrie Alush-Jaggs.

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29 April 2011 at 21:01 #5495
Colin Jacobs 1
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@colinjacobs1
Hacksaw slipping and marking work
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29 April 2011 at 21:01 #67706
Colin Jacobs 1
Participant
@colinjacobs1
Next up is the hacksaw I am using that slips whilst making the first cut ruining my work, how can I avoid this please?

Also How best to file the edges of my BMS plates so they are flat I either take too much off and leave a high spot in the middle but it seems to me the file is flat on the metal and should find its own level and flatten it for me.
29 April 2011 at 21:22 #67707
macmarch
Participant
@macmarch
Filing a flat and square edge is probably the most difficult thing to do. When I was a raw apprentice I was given a gauge and a rough cut block of mild steel. The gauge had a triangular hole, a square hole and a round hole all 1″” wide and high. The block had to be filed such that each side passed through the relevant hole with, ideally, no light showing.

I was given several blocks and a week to do it. I didn’t get it right but I can file flat and square. The hardest bit is to keep the file from dropping as you pass over the surface. I recommend that after you have worked on the flat surface for a while, turn the file and draw file. Errors will show instantly.
29 April 2011 at 21:40 #67708
The Merry Miller
Participant
@themerrymiller
I remember when I was at apprentice training school in the early 50’s we all had to make our own stiff joint calipers (inside and outside)

We were supplied with 1″ wide black mild steel 1/8″ thick and were told that the caliper blades had to be 1/16″ thick plus or minus 2 thou.

That was a killer because they were checked by the instructor and if any part of the blade was under size we had to start all over again
29 April 2011 at 21:57 #67710
Steve Garnett
Participant
@stevegarnett62550
Posted by Colin Jacobs 1 on 29/04/2011 21:01:53:

Next up is the hacksaw I am using that slips whilst making the first cut ruining my work, how can I avoid this please?

Okay, hacksawing:

First thing, after you’ve set the work up so that you are sawing across it, not down it, and it’s as close to the vice jaws as you can comfortably get, is how you hold the saw. What you should be doing is not just gripping it around the handle, but extending your first finger along the top of the frame. You’d be amazed at how much difference this makes to the lateral stability of any saw – it’s the easiest way of countering drift I know of. Without doing this, a hacksaw will twist around the handgrip very easily, and that’s the motion you are trying to avoid.

Second thing is where you stand. You want your eyes to line up vertically with the cut you are trying to make – that’s the only position from which you can correct any drift with certainty.

Thirdly, you have to make sensible use of your other hand. With your fingers on the rear of the vice, place your thumb against the side of the blade when you start to cut. Do this carefully so you don’t cut yourself. You now have a force from your cutting hand towards your thumb which is restraining it, and you can slide the blade back and forth across this.

Remember that you are only cutting on the forward stroke. Don’t try to force the blade down; let it do its own cutting. Make sure that the stroke you use uses as much of the blade as possible – short jerky strokes are far more likely to go astray and jump out of the cut than long smooth ones. During the cutting, try to keep the angle the saw makes relatively shallow – cuts like this are much easier to keep straight than high-angled ones, even though these sometimes appear to cut faster. The reason for the straighter cuts is that the cut itself is supporting more of the blade, so short-term drift is less likely.

Finally, don’t use el cheapo hacksaw blades. Use a reputable brand, like Eclipse. They cost more, but last far longer and are accordingly rather better value for money. If you are cutting steel, use a blade with a higher number of teeth per inch – for aluminium and other softer materials, use blades with less teeth and you won’t get so much clogging.

I don’t think that I’ve left out anything major, but there are enough smart people around here to point out any discrepancies if I have, I’m sure!

Edited By Steve Garnett on 29/04/2011 22:21:21
29 April 2011 at 23:02 #67713
mgj
Participant
@mgj
If it skids a bit to start with – it shouldn’t and probably one is using too coarse a saw – we all do. There are several ways round the problem. I’m told a bit of masking tape over the start works. I just use a fine triangular file (or the corner edge of the file I am about to use) to put a one stroke nick in the right place . That guides and the slighly deeper breadth in contact makes the problem go away.

Blade is in nice and tightly tensioned?

Are you talking about filing an edge or cleaning up? To clean up I use a fine cut mill file mostly, which should give a really good finish. Mind you, a bastard mill cut file is a pretty decent finishing tool too. Much better than the standard cross cut files. I just lay the mill file nearly along the work – takes all the bumps off very nicely.

The other trick is to file the bumps – since they are what one wants to remove – and not everything else as well. Use a straight edge to find them. If they are bad you just attack that bit. If small, draw file on the bump.

Edited By mgj on 29/04/2011 23:08:28

Edited By mgj on 29/04/2011 23:09:54
29 April 2011 at 23:07 #67714
Nicholas Farr
Participant
@nicholasfarr14254
Hi Colin, I’ll just add to steve’s post by saying that once you have made a start on the cut with the blade against your thumb, continue sawing but hold the front of the saw frame steady with your other hand, this will also help stop the blade bouncing out on the backstroke, but like Steve says, don’t put any pressure on the backstroke, just allow it to glide over. One other thing is having the blade quite taut in the frame, because if it is allowed to do a twisting action as you saw, it will tend to wander. You will also find it will need adjusting now and again, as it will stretch during use.

Filing does take practice, but one other way to stop you getting a hill on the ends of your plates, is to file the edges from one corner to the opposite corner for a short period, and then go between the other two corners and watching the different shade in the filing marks, so you can adjust the pressure more evenly. Just keep swapping for short periods of time until you have your desired result. Try not to get to impatient to get it finished in a hurry.

Regards Nick.

Edited By Nicholas Farr on 29/04/2011 23:09:49
30 April 2011 at 02:42 #67723
chris stephens
Participant
@chrisstephens63393
Hi Colin.

If there is a secret to filing, it must be to buy DECENT files. Even now I am amazed at the difference a good quality file can make. A cheap file seems to just slide over your work but a good file you can really feel bite. Oh and the best files are in my opinion “Oberg” from Bahco. They remove metal very quickly and can leave a finish that could be mistaken for ground, They are not cheap, about twice the price of Vallorbe, but they are worth every penny, or at least the ones I have are.

I hope they are not now made in China, with its concomitant quality concerns.

chriStephens
30 April 2011 at 10:02 #67734
Gordon W
Participant
@gordonw
All the above is true. Worth checking that the blade is in line with the saw frame and the blade mountings are a good fit in the frame, sometimes the blade can twist and make it impossible to cut straight. Oh, and practise.
30 April 2011 at 12:07 #67741
Colin Jacobs 1
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@colinjacobs1
Thanks for all the kind advice I am back in the workshop taking on board all comments.
30 April 2011 at 12:50 #67745
jomac
Participant
@jomac
I look closely at a file when I buy them, because even in a box of 20 most of them are NOT dead flat, ( thats what happens when they are outsouced to Asia), so its hard to file dead flat As to sawing, some one said, could have been Curley,??? to put the start mark right next to the vice jaws, use your thumb on the opposite side to steady the blade, then do an initial cut, move the round bar away from the jaws and keep cutting through, plus a bit off a tin can wrapped around the bar and held with a elastic band, and some of the tin held in the vice to stop it moving and to protect the bar, gives you an indicator to see if you are cutting off line, Worn cheap blades are notorious for not cutting straight, Get top quality It pays in the end.

John Holloway
30 April 2011 at 16:49 #67760
Steve Garnett
Participant
@stevegarnett62550
Posted by jomac on 30/04/2011 12:50:26:

… to put the start mark right next to the vice jaws, use your thumb on the opposite side to steady the blade, then do an initial cut, move the round bar away from the jaws and keep cutting through, plus a bit off a tin can wrapped around the bar and held with a elastic band, and some of the tin held in the vice to stop it moving and to protect the bar, gives you an indicator to see if you are cutting off line…

I’ve never found it necessary to go that far to get a hacksaw to cut properly!

One thing that you can do though is to invest in a pair of protective slip-over vice jaws. These reduce the possibility of the main jaws damaging the work very considerably. The real snag though with all of your moving it about is that if you have any amount of this to do, you are going to waste a staggering amount of time moving the work around and trying to realign all that tin – I’d say quite unnecessarily. But I’ve only been using hacksaws for 50 years…

The other thing that I was going to say about hacksawing in general is that even with expensive blades, it’s the set of them that generally goes first. At this point you can extend your blade life slightly by lubricating the cut, although it’s not really going to gain you an awful lot. Some of the spray-on silicon products are quite good for this, but I suspect that a lot of metalworkers will probably just use the ubiquitous WD40. I’ve not really got any evidence that always lubricating cuts will extend the life, but it may well make some cutting jobs easier, especially the ones where the cut releases stress in the material, and it closes up a bit.

Edited By Steve Garnett on 30/04/2011 16:55:37
30 April 2011 at 17:34 #67763
Raymond Anderson
Participant
@raymondanderson34407
Chris, Agreed, Sandvik Bacho are great files, another that you might like to try are PFERD,

I have used both types but decided to stick to only Pferd they are not so easily obtained as the Oberg’s and the price is similar [depends on the grade, as some are more expensive]

so if you see one buy it, you will not be disappointed [I hope].

Raymond.
30 April 2011 at 18:06 #67764
Dusty
Participant
@dusty
Tip of the day. I make no claim as to this being mine, it was in fact passed on to me by my Grandfather more years ago than I care to remember.

When sawing (this applies to whatever material you are sawing) repeat this little rhyme

“Hold on tightly, press on lightly”, this will give you three complete strokes of the saw.. This will give you a good rythmn for sawing and remind you of what you are supposed to be doing. Sawing faster may seem like a good idea, but all you will acheive is knackering yourself. Use the full length of the blade, it has teeth all the way along, use them.

As to files, I like to use a file that is slightly convex for roughing down as you are not cutting over the full width of material.

Vice jaws, a good way of protecting your work is to use a couple of pieces of 16g ali which you bend over the jaws. The other alternative is as a lot of toolmakers do.,discard the hard serated jaws and make up a set of mild steel ones. Do not throw away the serated jaws as they do have their uses.
30 April 2011 at 19:23 #67767
Steve Garnett
Participant
@stevegarnett62550
I used to have a pair of 4″ fibre vice jaw grips that were pretty good until they wore out. These mounted onto a bit of ally sheet that you could bend around the backs of the existing jaws. I believe they’re still available if you look around – I found a few on eBay.
30 April 2011 at 19:30 #67768
Nicholas Farr
Participant
@nicholasfarr14254
Posted by Steve Garnett on 30/04/2011 19:23:29:
I used to have a pair of 4″ fibre vice jaw grips that were pretty good until they wore out. These mounted onto a bit of ally sheet that you could bend around the backs of the existing jaws. I believe they’re still available if you look around – I found a few on eBay.

Hi Steve, Warco sell fibre ones on ally bases with magnets in them to hold them in place. Just look in the work holding section on thier online site.

Regards Nick.
1 May 2011 at 02:59 #67782
Ian S C
Participant
@iansc
The main file makes of any value here are Nicholson, and Whiltshire, we get allthe European hacksaw blades, plus our own brand Patience & Nicholson, who produce a very good product, along with drills and milling cutters.

I often use a bit of cardboard to protect the work in the vice. Ian S C
4 May 2011 at 13:27 #67976
Lawrie Alush-Jaggs
Participant
@lawriealush-jaggs50843
Hi Collin

A family friend gave me an excellent piece of advice for sawing wether wood or metal when I was about ten.

Keep your hand, wrist, elbow, shoulder and eye in the same line. Adjust your stance to accomplish this.

Let the saw do the work.

Use blades that are apropriate for the thickness of metal at hand. More teeth for thin stuff, fewer teeth for thick.

As to filing, use a linisher. Life is too short.

Lawrie
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