bent disc cutter

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Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Sun Nov 29, 15 11:46 pm Post subject: bent disc cutter

I have a disc cutter - Partner - 2 stroke - 12 " blade 6500 revs - about 25 years old but not done a lot of work.

I was on a roofing job around 20 years ago and the labourer put the machine down in front of the van. I drove off and ran over it ! which bent the cradle somewhat ! - also broke a plastic cover over the belt.

So I can make a new cover out of steel or possibly stainless and it would fit fairly easily because none of it is critical. BUT the cradle is aluminium tube and is bent quite badly so as to render the machine quite difficult to hold when it is running. It is Not broken. So my problem is : How do I bend aluminium tube back into shape ? I have found in the past taht heating ali does not render it workable in teh same way it would with steel, or even in annealing copper. - it just melts and falls apart !

It is about 20 mm diameter and I don't have any ali tube - but my mig is supposed to be able to weld ali.

I have copper tube and pipe benders - in 15 mm 20mm and 25 mm - do we think I can cut the ali and fix copper tube over it or inside it to restore the approx shape of the original ? either with pop rivets or self tappers ?

Option would be steel tube - which I would be comfortable working _ But is there any problem with steel or copper connected to aluminium ? - Bearing in mind the last thing I want is for the cradle to come apart in use !

edit spare cradles are not available to fit this machine - I bought one and it is completely differenmt due to design changes.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4613
Location: Lampeter

Posted: Sun Nov 29, 15 11:57 pm Post subject:
Getting a replacement cradle would be the ideal,even though its 25yrs old,have the design`s changed that much? If not possible,and the copper tube will fit in or over the Ali tube,i`d bore 2 holes through and bolt in preference to pop riveting or self tappers.

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Mon Nov 30, 15 12:06 am Post subject:

Ty Gwyn wrote:

Getting a replacement cradle would be the ideal,even though its 25yrs old,have the design`s changed that much?

If not possible,and the copper tube will fit in or over the Ali tube,i`d bore 2 holes through and bolt in preference to pop riveting or self tappers.

I agree Ty - replacement would be best - but Yes I have one from the same "model" but ten years younger and it is a shadow of teh one on mine - the fixing positions have changed by 6" ate ach end and mine has 3 fixings whereas teh "improved version has only two and is much shorter - altogether a clearly inferior system - but simply not useable - I guess your boltin right through is teh best way - and give the nuts a touch of weld to stop them shaking loose - but then we have 3 dissimilar metals in "electrical contact - and if I used stainless bolts I couldn't weld them - so I suppose I would have to use nylock nuts to try and keep them safe in all that vibration.

Hairyloon

Joined: 20 Nov 2008
Posts: 15464
Location: Today I are mostly being in Yorkshire.

Posted: Mon Nov 30, 15 12:35 am Post subject: Re: bent disc cutter

Falstaff wrote:

But is there any problem with steel or copper connected to aluminium ?

I would expect you to get galvanic corrosion, but I couldn't tell you how much of a problem that will cause you or how fast it'll cause it.
I think you should expect to never get your bolts undone again.

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Mon Nov 30, 15 2:17 am Post subject:
That's my opinion too HL - I'm not sure about the bolts - I have some M5 stainless bolts with nylock nuts - which I think would probably come undone, but if not I'll sheer them if neccesary. worth a try though I think - as long as I give them a good inspection each time I use it - plus I don't expect to get much moisture in the connections and whether that would help I rather think it would.

GrahamH

Joined: 23 May 2015
Posts: 523

Posted: Mon Nov 30, 15 3:40 am Post subject:

Falstaff, there is a paste available for joints between dissimilar metals to prevent galvanic corrosion. The paste is also waterproof.
I used to use it between combinations of copper, gun metal, bronze, aluminium and stainless.
Available at good electrical equipment suppliers.
Do not tape over the stainless nuts and bolts in an attempt to keep water out as the lack of oxygen will promote corrosion and cracks.

Last edited by GrahamH on Mon Nov 30, 15 3:45 am; edited 1 time in total

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Mon Nov 30, 15 3:44 am Post subject:

GrahamH wrote:

Thank you Graham - I do have electronic qualifications and therefore access to the wholesalers of that type of stuff - I'l go looking for it !

GrahamH

Joined: 23 May 2015
Posts: 523

Posted: Mon Nov 30, 15 3:48 am Post subject:
Falstatt, don't you sleep? 11:48 here...... See my edit in the previous post re stainless and corrosion. Another option for copper to other metal connections is to 'tin' the copper face of the joint. Basically that involves applying solder... CEF, City Electrical Factors sell Unial Electrical Jointing Paste but there are lots of other makes some of which sell in small tins/tubes. Try R.S.

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Mon Nov 30, 15 4:45 am Post subject:

GrahamH wrote:

Falstatt, don't you sleep? 11:48 here......

See my edit in the previous post re stainless and corrosion.

Another option for copper to other metal connections is to 'tin' the copper face of the joint.
Basically that involves applying solder...

CEF, City Electrical Factors sell Unial Electrical Jointing Paste but there are lots of other makes some of which sell in small tins/tubes.
Try R.S.

Sleep ? - occasionally

Thnks for the input - I'll take a look when the "wine weArs off"

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4613
Location: Lampeter

Posted: Mon Nov 30, 15 9:55 am Post subject:
If your worried about the nut`s coming undone,and welding a blob could be a problem,one sure way to stop the undoing is to cut a slot in the bolt with a junior hacksaw before assembly ,then splay the slot after tightening the nut.

GrahamH

Joined: 23 May 2015
Posts: 523

Posted: Mon Nov 30, 15 10:09 am Post subject:
Difficult cutting s/s bolts with hacksaw.....might be best to damage the threads with hammer and cold chisel.

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Mon Nov 30, 15 4:27 pm Post subject:
Forget the mig. The cost of sorting it out to weld ali would be more than the job is worth. You will need different gas, different wire & to change the liner in the torch. It will also take lots of practice to do.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Mon Nov 30, 15 5:05 pm Post subject:
A trick to bending aluminium and getting the heat just right is to rub the surface with tablet soap. As you heat the part the soap will eventually turn brown which just happens to be the point at which aluminium is most malleable but before it melts. However, it will lose any strength gained by prior heat treatment so this technique shouldn't be used on critical parts that have been heat treated.

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Mon Nov 30, 15 7:15 pm Post subject:

vegplot wrote:

A trick to bending aluminium and getting the heat just right is to rub the surface with tablet soap. As you heat the part the soap will eventually turn brown which just happens to be the point at which aluminium is most malleable but before it melts. However, it will lose any strength gained by prior heat treatment so this technique shouldn't be used on critical parts that have been heat treated.

That sounds fun - I might give that a try !

Mistress Rose

Joined: 21 Jul 2011
Posts: 16219

Posted: Tue Dec 01, 15 6:52 am Post subject:
You could use Loctite to keep the bolts from coming undone. I hate the stuff, but that is what it was designed for.

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