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Kennedy Hexacut Model 90

Worn guide slides

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Derek Reay20/05/2021 23:21:09
5 forum posts

Hi, I have one of the Kennedy Hexacut Model 90 powered hacksaws which I have been slowly restoring. I have now found that the twin guide slide rails are worn, and the gap between the rails varies by about 16 thou along the actual length of travel. It also looks as though both the blade frame, and also the top securing slide rail are also worn. In order to get the blade frame assembly to run fairly smoothly along the rails I have to have the 2 allen bolts somewhat loose. This means that there is some slop in the movement and the hacksaw frame will jump slightly at each end of its travel, and will not give a parallel cut.

Can I please ask if anyone has a solution to remedy this. I suppose each mating surface of the rails could be ground, but I would find that difficult to do. I also wondered whether some sort of Linear guides and carriages could be used.

Any advice would be welcome in order to obtain a more accurate cut.

Thank you.

AdrianR21/05/2021 08:03:53
538 forum posts
36 photos

Hi Derek,

I have a Model 60 with similar wear, and I have been trying to figure out how to fix it too. Recently there was another thread about a Hexacut 90 where someone showed pictures of milling the guides. I have not worked out how to mount the guides and frame on the mill so have not tried it yet.

I have been considering fabricating a new blade frame that at the top has a plate wider than the guides. Then on the plate create guides that work on the outside of the rails. For the guides, I am thinking of using small ball races.

My concern with this approach is the increase in the weight of the reciprocating parts.

I would be interested in how you fix yours.

Adrian

Ady121/05/2021 09:07:13
avatar
4562 forum posts
699 photos

You can buy new hex bar from ebay etc

Clive Foster21/05/2021 09:30:26
2735 forum posts
100 photos

Derek

If you have access to a mill that can handle the length simply mill the worn faces flat taking care to jig up or tilt the mill ing head at the correct angle. Might need to trim the flats on the blade carrier and top hexagon a touch too so there is sufficient gap for adjustment.

Its not exactly a precision machine to start with so lathe and mill bed accuracy isn't needed. Just nicely close.

I do wonder if stock hex bar would be accurate enough. Pretty sure that was all Kennedy used. Certainly the one I had dealings with showed no evidence of machining. Just plated and, methinks, left to wear in.

Obvious replacement is to go rooting around the round rail and slider bearing unit catalogues. For refurb a bit of fabrication to mount four round rails in place of the hex with four plain bearing, dry lubricated, sliders running on the bottom rails to carry the bow. X format bearing arrangement might be marginally more rigid but alignment good enough to exploit it will be a bear.

Were I to do the job I'd consider re-doing the whole thing with a new carrier and a triangular rail arrangement using larger rails. Two below for the bearings to run on and one on top for rigidity. Dashpot will be the least straightforward issue if re-engineering that way as the bow and frame will be heavier.

I'm a little surprised that no one has introduced an updated version exploiting modern components. Seems to me that the price could come in somewhere between the cheap baby bandsaws and the expensive Ferm et al ones with similar performance to the high end ones.

Clive

Dave Wootton21/05/2021 09:33:50
192 forum posts
51 photos

As Ady says hex bar is easily available, I had one of these many years ago, very worn through years of cutting through copper busbars. I can't remember the details but it was fairly easy to fabricate new guide frames. If I remember correctly one end of the hex guide was cast into an alloy pivot block. I replicated this by machining and fabricating the block from solid and turning hex bar down to a push fit in reamed holes in the block and locating it with grub screws, easy to align using the slider as a guide, nowadays I would use loctite retainer. It was a successful repair and the little saw worked quite well after, now long gone replaced by a chinese bandsaw.

Definitely worth repairing though, they chug away while you do other things, and it wasn't a huge job to do, all the milling was within the capacity of a ML7 and vertical slide.

Dave

Dave Halford21/05/2021 11:20:03
1590 forum posts
16 photos

Derek,

Like yours my 90 had to have the top slider quite loose to work, but that also allows the mains bars to get beaten up even more by the con rod action.

All I did was file off the front and back of the top slider at an angle where it clouted the wear ridges, which enabled both a decent clearance and a smooth bow travel (on mine at least) and a squarer cut than before

However as mentioned in the other Kennedy thread this week an ordinary hacksaw bimetal blade still does not cut straight.

Michael Gilligan21/05/2021 16:30:10
avatar
18325 forum posts
872 photos

For anyone interested ... Here’s Mr Kennedy’s patent : **LINK**

https://worldwide.espacenet.com/patent/search?q=pn%3DGB681620A

[ 3-dot menu at upper-right gives a download option ]

MichaelG.

john halfpenny21/05/2021 17:16:28
181 forum posts
25 photos

My Kennedy 60 cuts nice and square with a standard hacksaw blade, so I have never bothered with a deep blade. However mine has very little wear on the hex guide.

vic newey21/05/2021 17:50:30
87 forum posts
59 photos

I've just finished restoring mine, I stripped off the gobbed on bright green paint, sorted out the dashpot, removed black oil from off the belt etc. I seem to have been lucky with the rails as there is no play whatsoever. I even managed to cut a perfect 1mm off a 1" bar

After fine tuning it runs sweet as a nut so I'm well pleased. I made a short video of it running

**LINK**

Edited By vic newey on 21/05/2021 17:51:43

Dave Halford21/05/2021 19:22:17
1590 forum posts
16 photos
Posted by john halfpenny on 21/05/2021 17:16:28:

My Kennedy 60 cuts nice and square with a standard hacksaw blade, so I have never bothered with a deep blade. However mine has very little wear on the hex guide.

I've only heard the owners of 90's complain about blade wander. The bow is a lot bigger

Andy Stopford21/05/2021 21:26:44
88 forum posts
9 photos

See my album for milling Hexacut 60 guides - it's a bit of a fiddle setting them up, especially on a small mill, but easier than making a complete new arm assembly. The ideal would be just replacing the hexagonal bars, but its hard to see how they're fixed to the pivot block - as Dave Wooton suggests above, they may be cast into it.

Andy Stopford21/05/2021 21:43:19
88 forum posts
9 photos

Sorry, Adrian R, I hadn't noticed your pm. Set up with the face you're trying to machine parallel to the mill table (packed up with 1-2-3 blocks in my case), there is just enough clearance to end-mill the worn faces flat.

One side is quite easy to set up, the other harder because of the shape of the pivot block - I had to hang this over the end of the table:

sam_0380.jpg

It would be easier with slimmer clamps than these - I must get around to making some sometime.

Derek Reay23/05/2021 22:53:06
5 forum posts

Hello all, Firstly I would like to thank those members who have replied to my question regarding the worn slides on my powered hacksaw. Your comments are appreciated, and I am now considering which way forward I should attempt.

I have again looked at the Kennedy more closely over this weekend. It seems that size of each of the Hexagon bars on the twin slider unit, hacksaw frame, and the clamp only vary a few thou along their lengths. It is the gap between the inner sides of the twin rail slider guide rails that varies the most. It looks like one, or even both of the rails are bowed in more than one place. I will double check this with a longer straight edge. As such, the Hacksaw frame, when attached to the Twin Rail slider unit, with the top clamp, even with the bolts lightly tightened, the moving assembly will nip up. I have also noticed that when this unit is assembled there is a gap of about 100 thou between the bottom of the top clamp, and the top of the Hacksaw frame itself. So, could I ask whether there should be a gap, and, if so, how big should that gap be ? And secondly, should I try and open/close up the centre gap in the Twin rails to obtain a fairly constant sized gap. Or, should I attempt to set up a jig to mill or skim the insides of all the top and slide rails and the outsides of the hacksaw frame. I will have to be very careful here to ensure that all 60 degree angles are centred correctly to ensure the true hexagon shape is kept..

I am sorry if I have rambled on, but I have great difficulty with explaining things.. Also, I am still learning these model engineering practices.

Finally, I'm unsure as to whether the oil damper is correctly set up, as the adjustable Disk is very thin and only just covers the outer edges of the holes in the piston, and not the whole face of it. The disk is also very tight on the shaft of the adjusting bolt, so closing the gap over the holes is limited.

Once again, Thank you for your comments.

Dave Halford24/05/2021 11:39:06
1590 forum posts
16 photos

The two clamp bolts should have lock nuts, if not Loctitie them.

Derek Reay24/05/2021 18:41:21
5 forum posts

Hello Dave. Thank you for your comment. Yes, both clamp bolts pass through the Clamp and the Hacksaw Frame, which is threaded, and then locked up with lock nuts. I am unable to do them up tight as the whole assembly will nip up and definitely will not move at all. That is why I have to leave them slightly loose, which then allows the frame to rock from side to side and jump up at the end reaches of its travel.

Dave Halford24/05/2021 20:05:50
1590 forum posts
16 photos

It's like gib strips 'nearly tight' is required, maybe an 1/8 of a turn more will do it.

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