Disposable blades with Cambridge rocking microtome, anybody?

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pippo1234
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Disposable blades with Cambridge rocking microtome, anybody?

#1 Post by pippo1234 » Sun Feb 28, 2021 11:13 am

Hi,

I have just acquired a Cambridge "rocker" in very good condition, including the knife. After reading the excellent documentation of John B's (mrsonchus) adventures I am starting to think that was a mistake. If he found it hard to sharpen the knife, I stand no chance!

Has anybody found a way to use disposable blades with it? There was some mention of people having tried in the various thread, but I could not figure out if anybody had eventually succeeded. The Cambridge microtome is too bulky as a paperweight, though it has a beautiful retro look...

Thank you in advance.
Giulio

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#2 Post by MicroBob » Sun Feb 28, 2021 11:23 am

Hi Gulio,
the disposable blades are very thin and rely on a holder that firmly glamps them just behing the edge. So all DIY-attempts without such a blade holder won't work well. These blade holders are made by milling away a good part of a rectangular steel profile. This leads to unequal stesses in the steel and a curve in the holder. So it is not trivial to make such a holder. For bigger microtomes these holders turn up from timme to time, but they are probably to big for the cambridge rocker.

When you start with a good knife in good condition and have a honing guide (slips over the back of the knife) you might get along very well with the ridgid knives for your purposes.

Bob

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mrsonchus
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Re: Disposable blades with Cambridge rocking microtome, anybody?

#3 Post by mrsonchus » Sun Feb 28, 2021 11:48 am

Aha!
Things have changed since I posted re this excellent little 'tome. With the ability now to 3D print, and in a choice of materials with differing physical properties including strength, hardness, stiffness etc I suspect that the problem has an affordable solution.
The principle of a disposable-blade holder I'm 100% sure holds good for the rocking microtome. A scaled-down to fit version of those sold for std rotary microtomes would very likely be perfect. Basically a recreation of the shape and size of the steel blades that are used and have to be sharpened (with no need of course to consider the cutting edge) that has the ability to take and clamp a disposable (AKA replaceable) blade would be '3D printable' I'm sure? In my posts I demonstrated this idea by simply cellotaping a double-sized domestic men's razorblade to one of the steel knives - it cut great sections!
Think 3D-printed - If I had a 3D printer I'd make one for you but as yet I haven't had the nerve to jump onto that bandwagon!

The rocking microtome is really a very good device for sectioning prepared and embedded tissue - superior to hand-sectioning in my experience by a long way if that's what you intend to achieve. The making of permanent slides is the rocker's territory to my mind. Not only are reproducable sections possible but the very useful indeed ability to section in ribbons of serial sections for the study of tissue or the achievement of 'just the right vies' when slide-making....

If you aren't going to try to make mounted slides it may however be of limited use...
John B

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#4 Post by MicroBob » Sun Feb 28, 2021 1:20 pm

If I remeber right the blade holder of the rocking microtome is intended for fairly thin knives. This would make a thin blade holder necessary, not ideal for stiffness. But in steel it would probablx be possible ass stell has a high e-modulus. Plastics have a much lower e-modulus and in combination with the small thickness this would lead at best to a blade holder of limited use. 3D-printing of steel is possible today but very expensive because the parts are made from finely ground powder in a slow process. There are 3D-printing services that offer printing in a wide range of materials and you can get a quote by uploading a model.
I made a quick test: A blade holder 80mm long, 16mm wide, lower and upper part, just the wedge shapes, no threads, steps etc. would cost 250€ when printed from stainless steel, the only material there with a high e-modulus. There probably is a little room for improvement, but it will be roughly in this price range.
This is the print service I got this quote from: https://www.rapidobject.com/de/Wissensw ... _1173.html I have no experience with them and don't know whether there are cheaper or better services.

Bob

pippo1234
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Re: Disposable blades with Cambridge rocking microtome, anybody?

#5 Post by pippo1234 » Sun Feb 28, 2021 2:51 pm

If you aren't going to try to make mounted slides it may however be of limited use...
I guess you mean "unless you are willing to go through all the hard work necessary to embed in paraffin", it's not the right tool. Having got the message and googled some more I came across this http://www.microscopy-uk.org.uk/mag/ind ... para1.html and felt silly.

I was hoping to be able to ease into something like that in the long run by starting with carrot wedges or pith. If I understand what John means, though, not with the Cambridge or any serious microtome. I did try Dioni's Neuberg (both with one and two sellotape thicknesses) with terrible results. Nothing sticks in between the (new, branded) blades. Hence, when a Cambridge in excellent conditions came up for £45 I impulse-bought it.

Even in the long run, it seems that having a disposable blade holder 3D printed is going to put the total cost into second-hand rotary territory.

You live and learn I guess. May be I should start with the Brunel bench one or similar.

Many thanks for all the info.

I was forgetting to say. John, your latest posts were indeed inspirational. What beauty!

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#6 Post by mrsonchus » Sun Feb 28, 2021 3:54 pm

Have a look at my old post re this, the knife itself coul be used as the basis of a holder- drilled-holes, thin metal strip to clamb and a maybe a solution - on this post cellotape works!

Here's the start of this experiment -
John B

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#7 Post by MicroBob » Sun Feb 28, 2021 4:38 pm

With the rocking or rotary microtome you usually can't set the blade at an angle. With a sliding or many sledge microtomes this is possible. For paraffin a straight knife is fine, but for plant stems in carrot you would like to have a slicing cutting action. Compared to sectioning with hand microtome and blade holder sectioning fresh material with a sliding microtome is more reproducible. Some prefer hand microtome+ blade holder, some the sliding microtome.

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#8 Post by pippo1234 » Sun Feb 28, 2021 6:47 pm

Just as John's sellotape post and convinced me to hold onto the rocker as a long term, if space consuming, investment while starting with a hand microtome I realised the following.

Unlike the typical Cambridge and the Brunel rotaries, in this one the knife holder is bolted rather than cast. With the knife holder oriented the way I received it (see pictures), the knife is angled the wrong way (outward rather than towards the specimen) and the supplied object holder does not clear the knife. If I turn the knife holder 180* the knife is way too far from the object holder. Am I missing something obvious or ???

Image
Image

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#9 Post by MicroBob » Sun Feb 28, 2021 7:53 pm

Try to find out the difference between your microtome and this one: https://www.ebay.co.uk/itm/Vintage-Camb ... 4300529252
Normally therse should be a way to clamp the knife and adjust the clearance angle towards the specimen block. To fix the knife in an adjustable position a three-point contact is necessary, screw 1 against screw 2 and cast iron corner. So the screw pointing towards the block with its tip should be higher than the screw on the block side of the blade holder.
Is it possible that the specimen holder can be moved to give you more free room? The blocks won't all have the same size.
Whatever blade holder one would use it would have to resist the clamping forces without beeing gnawed away in no time.

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#10 Post by MicroBob » Sun Feb 28, 2021 8:21 pm

Is it possible to mount the blade holder the other way round?

pippo1234
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Re: Disposable blades with Cambridge rocking microtome, anybody?

#11 Post by pippo1234 » Sun Feb 28, 2021 9:32 pm

Exactly. Compared to that and any other Cambridge or clone I have seen the screws are reversed. The top ones point away from the specimen and viceversa for the bottom ones. Clearly the only way that makes sense is for the knife holder to be turned 180 degrees. Problem is, with that arrangement the knife blade is very far (3cm) from the tip of the specimen holder. And the specimen holder is meant to hold the paraffin block by melting (it has little holes currently full of wax). So it's not that there should be a wooden block in between. Either I have the wrong holder or there is something I am missing.

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#12 Post by pippo1234 » Wed Mar 03, 2021 9:38 am

I thought I'd complete this thread in case it can help somebody in the future.

Indeed the knife holder had to be reversed. As for the distance between the specimen holder and the knife, I carefully reread the following article.
http://www.microscopy-uk.org.uk/index.h ... tome1.html

and found this sentence:
"The holder (2) is much less convenient, firstly due to its inappropriate length. Even when it is installed at maximum depth on the rocking arm and the micrometer screw is in its lowest position, there’s still a large distance between the holder and the knife. That holder (2) requires for the sample paraffin block to be very high, as the lower samples mounted on it cannot reach the knife’s edge. "

Indeed, holder (2), which is the one I have, has a distance from the knife between 1.5 and 2cm (see first picture below) which does require >1.5cm of your paraffin block to be wasted. You can gain 1cm by extending it out (see second picture below). The top screw on the arm allows you to secure it in such a position as it controls the piston that puts pressure on the holder from inside.

Image
Image

Thanks Bob and John for your help!

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#13 Post by pippo1234 » Fri Apr 16, 2021 4:08 pm

I have been experimenting with the rocker on the side. I thought I might as well try how it would work with the OLFA LBB disposable blades that Bob recommends. They are the right size. I use the Cambridge knife for support without any need for sellotape. The knife holding screws hold the disposable blades securely against the knife. I let the disposable blade stick 2mm out relative to the knife.

I experimented with some FAA fixed (but not cleared/properly infiltrated, ) lichen embedded in wax. It was my first attempt with wax and there were some minor air gaps around the specimen. The wax block sectioned very nicely producing a very nice ribbon. I got a couple of decent sections, wet mounted them just to see and took a few pictures.

The Cambridge rocker definitely produces good cuts of the wax block with the disposable blades. Whether the resulting specimen sections can be good enough without full processing and proper infiltration remains to be seen. I'd say that, given that there is ample room for improvement in my embedding technique, there is promise.

Image
Image
Last edited by pippo1234 on Fri Apr 16, 2021 9:29 pm, edited 1 time in total.

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mrsonchus
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Re: Disposable blades with Cambridge rocking microtome, anybody?

#14 Post by mrsonchus » Fri Apr 16, 2021 7:13 pm

Hi, very nice cuts to my eyes!

The rocker is a fine little machine - your sections are certainly as good as any of the best hand-sections you'll see. It all depends on what you want to achieve as far as infiltration and embedding goes.

Congratulations, things are going well!
John B

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Re: Disposable blades with Cambridge rocking microtome, anybody?

#15 Post by MicroBob » Sat Apr 17, 2021 7:11 am

Congratulations, nice sections!
The OLFA LBB blades have two bevels per side, the final micro bevels including an angle of probably 35°. So the body of the blade should be in a bit more than 17,5° to the movement plane of the block.

Bob

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